target: add set_connection()

Add a method to set the connection for the current thread within the
target. This method returns the connection that was previously set.

devlib/target.py

@@ -313,6 +313,12 @@ def get_connection(self, timeout=None):
             raise ValueError('Connection class not specified on Target creation.')
         return self.conn_cls(timeout=timeout, **self.connection_settings)  # pylint: disable=not-callable
 
+    def set_connection(self, conn):
+        tid = id(threading.current_thread())
+        old_conn = self._connections.get(tid)
+        self._connections[tid] = conn
+        return old_conn
+
     def wait_boot_complete(self, timeout=10):
         raise NotImplementedError()
 

doc/target.rst

@@ -184,6 +184,13 @@ Target
              blocking operation (e.g. using ``background()``) while at the same
              time doing something else in the same host-side thread.
 
+.. method:: Target.set_connection(conn)
+
+   Set the Target's connection for the current thread to the one specified
+   (typically, one that has previously been returned by the call to
+   ``get_connection``). Returns the old connection to the current thread -- it
+   is up to the coller to keep track of it and restore it if they wish.
+
 .. method:: Target.setup([executables])
 
    This will perform an initial one-time set up of a device for devlib