LU-7070 tests: Skip sanity 24x based on server version

LU-7070 tests: Skip sanity 24x based on server version

sanity test 24x tests cross MDT rename and link. Cross-MDT
rename and link was added to Lustre after the 2.7.55 tag. Thus,
only run sanity 24x for server version 2.7.56 or later.

Signed-off-by: James Nunez <james.a.nunez@intel.com>
Change-Id: I0c2e8c8581b8499ec7f1a25092b17be29aa49c1e
Reviewed-on: http://review.whamcloud.com/17990
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Wei Liu <wei3.liu@intel.com>
Reviewed-by: Saurabh Tandan <saurabh.tandan@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>