Changed the supervisord config to tie the Phabricator daemon lifecycle to the supervisord lifecycle.
Changed the supervisord config to tie the Phabricator daemon lifecycle to the supervisord lifecycle.

1. When supervisord starts up, we call "phd start" to launch the Phabricator daemons
2. When supervisord stops, we call "phd stop" to shut down the Phabricator daemons

This replaces previous logic which just ran continuously and ensured that the daemons were running.

This change is prompted by two discoveries:

1. The Phabricator daemons don't seem to be having any issues with staying up, so only the first
   call to "phd start" actually does anything, while the others all polute the logs with warnings.
2. The Phabricator daemons will take a lock in the MySQL instance, and other deamons will refuse
   to run if that lock is being held. This means that if a daemon is running while the VM is torn
   down, then it can leave the MySQL instance in a state where other daemons will refuse to start.
   In this case, the only fix is to restart the MySQL instance. To avoid this, we should shut down
   the daemons when we get a lifecycle event indicating the VM is about to die.

google/appengine-phabricator,google/appengine-phabricator,google/appengine-phabricator