When starting a new session the agent waits a certain time for the new Xvnc to start responding on the proper VNC port. If this doesn't happen a failure is reported to the master and another agent is tried.
However this method assumes that the timeout happens because the session has failed to start. It might be the case that the session just took too long to start up. At that point the agent will have a running session that the master is unaware of, and that can cause issues for applications that don't work well with multiple sessions.
We should probably try to clean up the session when we hit the timeout.
The agent logs the following when this timeout hits:
> 2018-05-29 13:59:03 WARNING vsmagent.session: Xvnc start for username user0 failed (timeout waiting for vnc port)