More helpful rendering of stale snapshots

[stephencelis]

Right now we get a list like this:

- "/path/to/my/snapshot"
- "/path/to/my/other/snapshot"

This isn't super actionable. I've changed the formatting to this:

  "/path/to/my/snapshot" \
  "/path/to/my/other/snapshot"

That way we can copy these lines and paste them after an rm in a console.

[mbrandonw]

good idea!