Rework the way we create sharded repositories within the svnadmin command-
line tests.  Instead of hardcoding different 'db/format' contents for
different (server_minor_version, fs_type) test constraints, achieve the
same by using a separate helper function.  Do not attempt to generalize
this logic, because right now we only require this in a couple of tests.

* subversion/tests/cmdline/svnadmin_tests.py
  (write_sharded_format): New.  Patches the 'db/format' contents of the
    repository filesystem so that it would use the specified sharded layout.
    Strictly speaking, calling chmod() here is not currently required,
    because we make all test repositories world-writeable as a part of the
    their initialization.  However, this helper should also work for the
    repositories that were created indirectly, e.g. via 'svnadmin create'.
    These repositories would contain a read-only 'db/format' file, hence we
    would fail to patch it without preparative permission juggling.
  (hotcopy_incremental_packed, verify_packed, fsfs_hotcopy_progress):
    Simplify these tests by utilizing the new helper.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1615541 13f79535-47bb-0310-9956-ffa450edef68