repopick: Update script with some fixes

Make quiet actually be quiet.
Allow overriding the path for a repopick.
Sort query and topic results to have a better chance of them applying
cleanly.
Don't try to pull from github when using a custom gerrit address.
Catch git command failures and properly return failure codes.

Change-Id: I7ff010fbfbf1026c6fe03cb27649f677637e1bb5