Init missing repositories, better failure reporting

[promovicz]

This patch makes it possible to mirror organizations with repositories that are broken or blacklisted by github.

This is done by continuing on failure. Failed repositories will be printed on finish.

(if you don't like the messages or other details then please drop a line)

[promovicz]

Oh, and I forgot: this also makes "sync" initialize repos that aren't present properly.

This way its easier to mirror incrementally, even if the set of repositories changes.