Increase disk size

The based image default is 10GB which is insufficient for a single large repository like www-gitlab-com to be repacked, or even moved to a different shard since the host operating takes up space too.

The gitlab and gitaly-n nodes are now set to 250GB to provide sufficient space to move a large repo from the default storage after doing a simple Omnibus install to the HA Gitaly cluster.

Closes #2583 (closed)