Fix for deadlock in event processor.
Fix for deadlock in event processor.

If the main event loop throws an exception, we could wind up in a
deadlocked situation because the condition variable is never released.

matt-deboer/marathon-lb,vixns/marathon-lb,mesosphere/marathon-lb,vixns/marathon-lb,matt-deboer/marathon-lb,matt-deboer/marathon-lb,mesosphere/marathon-lb,vixns/marathon-lb,mesosphere/marathon-lb