ftests: Add cgget test with multiple '-r' flags

ftests: Add cgget test with multiple '-r' flags

Add a test that exercises multiple '-r' flags passed
into cgget.  This test verifies the following cgget
operation:

	$ cgget -r memory.limit_in_bytes -r memory.soft_limit_in_bytes \
	  008cgget
	008cgget:
	memory.limit_in_bytes: 1048576
	memory.soft_limit_in_bytes: 1024000

-----------------------------------------------------------------
Test Results:
        Run Date:                          Feb 09 20:48:45
        Passed:                                  1 test(s)
        Skipped:                                 0 test(s)
        Failed:                                  0 test(s)
-----------------------------------------------------------------
Timing Results:
        Test                                    Time (sec)
        ---------------------------------------------------------
        setup                                        18.71
        008-cgget-multiple_r_flags.py                 0.78
        teardown                                      0.00
        ---------------------------------------------------------
        Total Run Time                               19.49

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