PCT-637: Query Analytics does not handle MySQL Restart

http://tools-ci.percona.com/job/percona-agent-branch/28/console
The behavior I mean is just: try to send signal, timeout after 1 second.  Chan should be buffered, but re a previous comment I think buf should be 1 because we don't want to queue multiple restart notifications.  Listener should always receive each signal; if not, something is wrong.