Fix volumes-from re-applying on each start

Fixes #9709
In cases where the volumes-from container is removed and the consuming
container is restarted, docker was trying to re-apply volumes from that
now missing container, which is uneccessary since the volumes are
already applied.

Also cleaned up the volumes-from parsing function, which was doing way more than
it should have been.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>