LU-11499 tests: skip test_56ba for old server

LU-11499 tests: skip test_56ba for old server

sanity test_56ba exercise 'lfs find' options expanded
for Progressive File Layout feature.
Patch skips test_56ba for old MDS where PFL feature
does not exist.

Test-Parameters: trivial
Signed-off-by: Elena Gryaznova <c17455@cray.com>
Cray-bug-id: LUS-5536
Reviewed-by: Alexander Boyko <c17825@cray.com>
Reviewed-by: Vladimir Saveliev <c17830@cray.com>
Change-Id: I2439663008548b89c78d0d3f13f3c0722c8f9ba7
Reviewed-on: https://review.whamcloud.com/33344
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alexandr Boyko <c17825@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>