With this change mergeinfo.py gets more useful. There is
a distinction between merges and follow-up CLs/ports/reverts.

Also the information is show if the commit is already
rolled/an lkgr/deployed to Canary channel.

Additionally some formatting errors were resolved and
the already existing git wrapper used.

LOG=N
R=machenbach@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/1341303002

Cr-Commit-Position: refs/heads/master@{#31043}