LU-5276 build: handle RHEL ldiskfs series more accurated

LU-5276 build: handle RHEL ldiskfs series more accurated

Since RHEL7 change RHEL_RELEASE macro format. So we need
a unified way to handle it. Change using RHEL_MAJOR &
RHEL_MINOR to decided which ldiskfs series to be choose.

Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Change-Id: I147c4ff01372f4aafcdbce6197c7a85e9d64027b
Reviewed-on: http://review.whamcloud.com/11398
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Minh Diep <minh.diep@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>