bitbake: event/command: Allow UI to request the UI eventhander ID

The UI may want to change its event mask however to do this, it needs the
event handler's ID. Tweak the code to allow this to be stored and add
a command to query it.

Use the new command in the process server backend.

(Bitbake rev: f8cf2cb58b80ce74f756a11a9773b6b0e78d51ee)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/server/process.py

@@ -63,7 +63,12 @@ class ServerCommunicator():
                 pass
 
     def getEventHandle(self):
-        return self.event_handle.value
+        handle, error = self.runCommand(["getUIHandlerNum"])
+        if error:
+            logger.error("Unable to get UI Handler Number: %s" % error)
+            raise BaseException(error)
+
+        return handle
 
 class EventAdapter():
     """