Include verbose output of `git map-branches` to make visible what the
state of the different branches is.

R=iannucci@chromium.org

Change-Id: I4af03ef15b39e4ba84a41c01d1ec801e7bb4bbd6
Reviewed-on: https://chromium-review.googlesource.com/c/1360711Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>