LU-13148 tests: clean up sanity 56ra add debugging

LU-13148 tests: clean up sanity 56ra add debugging

Consolidate duplicate code from sanity.sh test_56ra() into a
helper function to make it easier to see what is being run.

Print out the before and after values for each test.

Skip test_56ra for versions older than 2.12.4, since it was
backported in commit v2_12_3-24-gd55982d842.

Test-Parameters: trivial testlist=sanity env=ONLY=56ra,ONLY_REPEAT=50
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ia28c1b556f53ea88643805cbf4ada725a53ebbe5
Reviewed-on: https://review.whamcloud.com/38021
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>