test_ldap: Do not uses pytest fixtures as functions
    
    test_ldap.py::test_local_negative_timeout_enabled_by_default
      /usr/lib/python3.7/site-packages/_pytest/fixtures.py:827:
        RemovedInPytest4Warning: Fixture "passwd_ops_setup" called directly.
        Fixtures are not meant to be called directly, are created
        automatically when test functions request them as parameters. See
        https://docs.pytest.org/en/latest/fixture.html for more information.
        res = fixturefunc(**kwargs)
      /usr/lib/python3.7/site-packages/_pytest/fixtures.py:827:
        RemovedInPytest4Warning: Fixture "group_ops_setup" called directly.
        Fixtures are not meant to be called directly, are created
        automatically when test functions request them as parameters. See
        https://docs.pytest.org/en/latest/fixture.html for more information.
        res = fixturefunc(**kwargs)
      /usr/lib/python3.7/site-packages/_pytest/fixtures.py:827:
        RemovedInPytest4Warning: Fixture "user_and_group_rfc2307" called directly.
        Fixtures are not meant to be called directly, are created
        automatically when test functions request them as parameters. See
        https://docs.pytest.org/en/latest/fixture.html for more information.
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3942
    
    Merges: https://pagure.io/SSSD/sssd/pull-request/3953