Switch from upstart to os-refresh-config for MySQL server-id's

This is both more reliable, and more cross-platform. With the
mysql element, this upstart job is never run, as a sysvinit rather
than upstart job triggers mysql.

Change-Id: I208310048d7617ec7726eceee9e4e269f1473510
Merge "Switch from upstart to os-refresh-config for MySQL server-id's"