repopick: Allow picking batch of commits with the same Change-Id

Gerrit does allow assigning the same Change-Id for multiple commits. This patch allows picking them properly.

Change-Id: Idedc64f58eebe41a0d212c72329d15acff24efb9
repopick: Don't redirect stdout on --quiet

For some reason, when --quiet is specified (example:
repopick --quiet -c 7834), git ends up in /home instead
of the actual repository.

This is a quick workaround until a proper solution is found

Change-Id: I60e0f684909a23b557ee3147b8954b71be995319