ftests: Add a cgset test with multiple '-r' flags and cgroups

ftests: Add a cgset test with multiple '-r' flags and cgroups

Add a cgset test that provides multiple '-r' flags to multiple
cgroups.

-----------------------------------------------------------------
Test Results:
        Run Date:                          Mar 08 19:30:43
        Passed:                                  1 test(s)
        Skipped:                                 0 test(s)
        Failed:                                  0 test(s)
-----------------------------------------------------------------
Timing Results:
        Test                                    Time (sec)
        ---------------------------------------------------------
        setup                                        15.33
        026-cgset-multiple_r_multiple_cgroup.py       5.14
        teardown                                      0.00
        ---------------------------------------------------------
        Total Run Time                               20.47

Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>