Fix a failure in a test that is skipped on Windows by using the sandbox
in a more standard way.

* subversion/tests/cmdline/svnsync_authz_tests.py
  (basic_authz,
   copy_from_unreadable_dir,
   copy_with_mod_from_unreadable_dir): Use generated names for sbox.
  (copy_with_mod_from_unreadable_dir_and_copy): Build sbox.
  (specific_deny_authz): Use generated name.
  (copy_delete_unreadable_child): Use generated name. No working copy.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1552137 13f79535-47bb-0310-9956-ffa450edef68