cit: Add ability to select infra branch.
cit: Add ability to select infra branch.

TBR=hinoka@chromium.org
BUG=None
TEST=local
  - Ran with different branches, seems to work.

R=hinoka@chromium.org

Review URL: https://codereview.chromium.org/1414223003

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@297284 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools