Add two tests for the 'svnauthz --groups-file' behavior.  Follow-up to r1438407.

* subversion/tests/cmdline/svnauthz_tests.py
  (svnauthz_accessof_groups_repo_test, svnauthz_accessof_groups_file_test):
    New tests.
  (test_list): Add new tests.

Patch by: Evgeny Kotkov <evgeny.kotkov{_AT_}visualsvn.com>