Check for stale PID lock when starting

The PID lock file does not actually test whether the lock is valid during
acquisition.  This leads to a failure to acquire the lock (essentially just
a file-based lock) when starting the process after a failure / kill.

Change-Id: Iebf0e077377278eb28b3280a8abfc605ac68a759
Merge "Check for stale PID lock when starting"