GCE: use our own lighter MySQL Docker image.

Use systemd/CoreOS instead of supervisor,
Less InnoDB memory,
No snapshots,
unrelated to Docker image: keep data files on CoreOS /var/lib/mysql-camli so
they persist across reboots.

Change-Id: Ib903c386fb3e2df0b7cf2d3eb466290f2b16f94b