Check docker/volume compatibility with remotes

[eschrock]

Expected Behavior

If I try to pull from a remote that is incompatible with my current repository, I should get a clean error.

Actual Behavior

We'll happily try to pull down volumes even if they don't make sense (e.g. cloning a "v1" that doesn't exist).

Steps to Reproduce the Problem

Create a repo with multiple volumes (like mongo) and push to a remote. Create a new repo with a single volume (like postgres), add the remote, and pull.

Version

0.3.1

Additional Information

There is some ambiguity about what "compatible" means. At a mimum, I'd say it should be that number of volumes, and their mappings into the container, is consistent. A slightly more strict version would be that they are derived from the same image tag, though without a way to control that it may be annoying. A super strict version is that the docker config has to match exactly.