Adding -u and -f as short options for --upload and --force.
There is precedent for these short options elsewhere in
git_cl.py

TBR=maruel@chromium.org

Review URL: https://chromiumcodereview.appspot.com/11783007

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@175310 0039d316-1c4b-4281-b951-d872f2087c98