LU-11797 tests: improve sanity test 272a checking

LU-11797 tests: improve sanity test 272a checking

Improve sanity.sh test_272a() to check data integrity before it
checks the stripe count.  Also, print out the stripe count if it
does not match our expectations.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I75397f251f10ed00c3dea9f80243d7ba9eacab07
Reviewed-on: https://review.whamcloud.com/33889
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>