Teach the cmdline tests to use a pre-cooked version of FSFSv4.

* subversion/tests/templates/empty-fsfs-v4.zip: New.
* subversion/tests/cmdline/svntest/main.py
  (_parse_options): Add minor-version tweak for pre-cooked FSFSv4 repository.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1619748 13f79535-47bb-0310-9956-ffa450edef68