Docker ctl script isn't compatible with overlay2 installations

[bstick12]

The docker ctl script attempts to umount overlay mounts but not overlay2 mounts.

I also see with the latest version that a new mount is created by docker at /var/vcap/store/docker/docker this needs to be umount as well.

If you deploy with a persistent volumes in AWS. When you don't umount the /var/vcap/store/docker/docker as part of the shutdown. BOSH will attempt to umount the device but since there are two mounts only one will be removed. This causes the recreate to fail.

worker/985839b3-cb45-4597-911b-0886c2f7b344:/var/vcap/sys# mount | grep xvdf1
/dev/xvdf1 on /var/vcap/store type ext4 (rw,relatime,data=ordered)
/dev/xvdf1 on /var/vcap/store/docker/docker type ext4 (rw,relatime,data=ordered)