High availability CS

[chrisburr]

As we're going to prefer loading the CS from a remote git URL it would be nice to support multiple sources. This could be done by supporting a list of values in the environment variable.

Things to consider:

• One or more sources should be allowed to fail cloning/pulling
• Use the same local repo for multiple sources with different remotes
• All sources must have the same initial commit
• If there are valid sources, the "deepest" commit should be prefered