How to use the execnet.gateway_bootstrap.bootstrap function in execnet

spec = self.defaultspec
        if not isinstance(spec, XSpec):
            spec = XSpec(spec)
        self.allocate_id(spec)
        if spec.execmodel is None:
            spec.execmodel = self.remote_execmodel.backend
        if spec.via:
            assert not spec.socket
            master = self[spec.via]
            proxy_channel = master.remote_exec(gateway_io)
            proxy_channel.send(vars(spec))
            proxy_io_master = gateway_io.ProxyIO(proxy_channel, self.execmodel)
            gw = gateway_bootstrap.bootstrap(proxy_io_master, spec)
        elif spec.popen or spec.ssh or spec.vagrant_ssh:
            io = gateway_io.create_io(spec, execmodel=self.execmodel)
            gw = gateway_bootstrap.bootstrap(io, spec)
        elif spec.socket:
            from execnet import gateway_socket

            io = gateway_socket.create_io(spec, self, execmodel=self.execmodel)
            gw = gateway_bootstrap.bootstrap(io, spec)
        else:
            raise ValueError("no gateway type found for {!r}".format(spec._spec))
        gw.spec = spec
        self._register(gw)
        if spec.chdir or spec.nice or spec.env:
            channel = gw.remote_exec(
                """
                import os
                path, nice, env = channel.receive()
                if path:
                    if not os.path.exists(path):

If no spec is given, self.defaultspec is used.
        """
        if not spec:
            spec = self.defaultspec
        if not isinstance(spec, XSpec):
            spec = XSpec(spec)
        self.allocate_id(spec)
        if spec.execmodel is None:
            spec.execmodel = self.remote_execmodel.backend
        if spec.via:
            assert not spec.socket
            master = self[spec.via]
            proxy_channel = master.remote_exec(gateway_io)
            proxy_channel.send(vars(spec))
            proxy_io_master = gateway_io.ProxyIO(proxy_channel, self.execmodel)
            gw = gateway_bootstrap.bootstrap(proxy_io_master, spec)
        elif spec.popen or spec.ssh or spec.vagrant_ssh:
            io = gateway_io.create_io(spec, execmodel=self.execmodel)
            gw = gateway_bootstrap.bootstrap(io, spec)
        elif spec.socket:
            from execnet import gateway_socket

            io = gateway_socket.create_io(spec, self, execmodel=self.execmodel)
            gw = gateway_bootstrap.bootstrap(io, spec)
        else:
            raise ValueError("no gateway type found for {!r}".format(spec._spec))
        gw.spec = spec
        self._register(gw)
        if spec.chdir or spec.nice or spec.env:
            channel = gw.remote_exec(
                """
                import os

spec.execmodel = self.remote_execmodel.backend
        if spec.via:
            assert not spec.socket
            master = self[spec.via]
            proxy_channel = master.remote_exec(gateway_io)
            proxy_channel.send(vars(spec))
            proxy_io_master = gateway_io.ProxyIO(proxy_channel, self.execmodel)
            gw = gateway_bootstrap.bootstrap(proxy_io_master, spec)
        elif spec.popen or spec.ssh or spec.vagrant_ssh:
            io = gateway_io.create_io(spec, execmodel=self.execmodel)
            gw = gateway_bootstrap.bootstrap(io, spec)
        elif spec.socket:
            from execnet import gateway_socket

            io = gateway_socket.create_io(spec, self, execmodel=self.execmodel)
            gw = gateway_bootstrap.bootstrap(io, spec)
        else:
            raise ValueError("no gateway type found for {!r}".format(spec._spec))
        gw.spec = spec
        self._register(gw)
        if spec.chdir or spec.nice or spec.env:
            channel = gw.remote_exec(
                """
                import os
                path, nice, env = channel.receive()
                if path:
                    if not os.path.exists(path):
                        os.mkdir(path)
                    os.chdir(path)
                if nice and hasattr(os, 'nice'):
                    os.nice(nice)
                if env:

spec = self.defaultspec
        if not isinstance(spec, XSpec):
            spec = XSpec(spec)
        self.allocate_id(spec)
        if spec.execmodel is None:
            spec.execmodel = self.remote_execmodel.backend
        if spec.via:
            assert not spec.socket
            master = self[spec.via]
            proxy_channel = master.remote_exec(gateway_io)
            proxy_channel.send(vars(spec))
            proxy_io_master = gateway_io.ProxyIO(proxy_channel, self.execmodel)
            gw = gateway_bootstrap.bootstrap(proxy_io_master, spec)
        elif spec.popen or spec.ssh:
            io = gateway_io.create_io(spec, execmodel=self.execmodel)
            gw = gateway_bootstrap.bootstrap(io, spec)
        elif spec.socket:
            from execnet import gateway_socket
            io = gateway_socket.create_io(spec, self, execmodel=self.execmodel)
            gw = gateway_bootstrap.bootstrap(io, spec)
        else:
            raise ValueError("no gateway type found for %r" % (spec._spec,))
        gw.spec = spec
        self._register(gw)
        if spec.chdir or spec.nice or spec.env:
            channel = gw.remote_exec("""
                import os
                path, nice, env = channel.receive()
                if path:
                    if not os.path.exists(path):
                        os.mkdir(path)
                    os.chdir(path)

if spec.execmodel is None:
            spec.execmodel = self.remote_execmodel.backend
        if spec.via:
            assert not spec.socket
            master = self[spec.via]
            proxy_channel = master.remote_exec(gateway_io)
            proxy_channel.send(vars(spec))
            proxy_io_master = gateway_io.ProxyIO(proxy_channel, self.execmodel)
            gw = gateway_bootstrap.bootstrap(proxy_io_master, spec)
        elif spec.popen or spec.ssh:
            io = gateway_io.create_io(spec, execmodel=self.execmodel)
            gw = gateway_bootstrap.bootstrap(io, spec)
        elif spec.socket:
            from execnet import gateway_socket
            io = gateway_socket.create_io(spec, self, execmodel=self.execmodel)
            gw = gateway_bootstrap.bootstrap(io, spec)
        else:
            raise ValueError("no gateway type found for %r" % (spec._spec,))
        gw.spec = spec
        self._register(gw)
        if spec.chdir or spec.nice or spec.env:
            channel = gw.remote_exec("""
                import os
                path, nice, env = channel.receive()
                if path:
                    if not os.path.exists(path):
                        os.mkdir(path)
                    os.chdir(path)
                if nice and hasattr(os, 'nice'):
                    os.nice(nice)
                if env:
                    for name, value in env.items():