Add meta=filerepoinfo for getting file repo info

We currently only return the image repository name for imageinfo, which
is not particularly useful, especially since image repositories aren't
accessible via the API. This patch adds meta=filerepoinfo, which will
return a list of repositories and relevant information (like the API URL
for ForeignAPIRepo ones)

Also returns the local repo now, and defaults to "all" in a more useful
fashion.

Change-Id: I1aaed0895d2a0bc224c82e93975ecf6afd8cb6b8
Merge "Add meta=filerepoinfo for getting file repo info"