mysql cart: user-settable start timeout

Increase startup timeout for MySQL cart to 45 seconds, allow setting
`start` timeout via `OPENSHIFT_MYSQL_START_TIMEOUT` user env var and
`stop` timeout via `OPENSHIFT_MYSQL_STOP_TIMEOUT`.

Enterprise bug 1106450
https://bugzilla.redhat.com/show_bug.cgi?id=1106450