It is inspired by src/tools/roll_swarming_client.py but generalized.

R=dpranke@chromium.org, stip@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1147033003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@295386 0039d316-1c4b-4281-b951-d872f2087c98