This CL adds information to the git map-branches command. Invoking 
it map-branches with -v, will show tracking status of branches and
invoking with -vv will additionally show the Rietveld URL and the
branch hash.

BUG=None

Review URL: https://codereview.chromium.org/509843002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@291776 0039d316-1c4b-4281-b951-d872f2087c98