This is the bare beginnings of Gerrit support for (non-repo) depot_tools,
based on Roland's work.
Differnt from http://codereview.chromium.org/8826015/
 it read codereview.settings and if it has GERRTI_HOST and GERRIT_PORT,
 then "git cl config" configured it for gerrit.
   installs hooks/commit-msg
   git config gerrit.host $GERRIT_HOST
   git config gerrit.port $GERRIT_PORT

 if it has gerrit.host config, "git cl upload" will upload a change
 to gerrit as
   "git push --receive-pack=... origin master"
 it scans description and extract reviewers from R= line.

Review URL: http://codereview.chromium.org/9264065

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@120276 0039d316-1c4b-4281-b951-d872f2087c98