LU-1812 ldiskfs: detect generated utsrelease.h

Fix lustre-ldiskfs.spec.in to use SLES11's generated header files.

Signed-off-by: James Simmons <uja.ornl@gmail.com>
Signed-off-by: chas williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Change-Id: I0eb198274015bfd38c48e9f68ceb15fe9e601d17
Reviewed-on: http://review.whamcloud.com/5188
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>