I am too lazy to setup a Gerrit instance locally that matches
production. This add a "test" bundle which solely has the
"test/gerrit-ping" repository.

Example usage:

  $ ./branch.py --delete --abandon --bundle test REL1_19
  Created https://gerrit.wikimedia.org/g/test/gerrit-ping/+/refs/tags/REL1_19 [ebdc5b946fa15ed9e8cfcbe69c568e7ee5a244f6]
  Deleting branch REL1_19 in test/gerrit-ping