LU-12560 tests: Use full path for test-groups

LU-12560 tests: Use full path for test-groups

Acceptance-small doesn't use the full path when accessing
the test-groups directory, so it will only run when
executed from the directory containing test-groups.

Correct it to use the full path, so it can be run from any
directory.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I788b2993e8b9a5e83e18940aae503fb21ade9cdc
Reviewed-on: https://review.whamcloud.com/35541
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>