Lvm setup and wait for socket

This is based on the PR #24, please merge it first. There is only commit specific to this PR.

First this fixes [bug 985832](https://bugzilla.mozilla.org/show_bug.cgi?id=985832) mounting all available instance storage on `/mnt/` using LVM.

And as bonous I fixed [bug 990287](https://bugzilla.mozilla.org/show_bug.cgi?id=990287) which would likely have caused more issues as formatting the disk makes docker startup take a little extra time, or 10s-30s or so - don't have exact measurements.

**Note**, I didn't run a test to see if `/var/run/docker.sock` was indeed missing. But log output shows that `docker-worker.log` prints out `"Waiting for /var/run/docker.sock"`, and have I haven't been getting issues with first task failing since I introduced this. So a qualified guess says that missing `docker.sock` was indeed the cause of [bug 990287](https://bugzilla.mozilla.org/show_bug.cgi?id=990287).