init: hide summary output when using --quiet

Change-Id: I5e30a6d6a1c95fb8d75d8b0f4d63b497e9aac526
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/256452


Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Mike Frysinger <vapier@google.com>