LU-2391 build: separate lustre-osd-[ldiskfs,zfs] RPMs

LU-2391 build: separate lustre-osd-[ldiskfs,zfs] RPMs

Add support for separate lustre-osd-[ldiskfs,zfs] RPMs creation in
lustre.spec.in template. This will prevent osd_[ldiskfs,zfs].ko
modules from being shipped as part of lustre-modules RPM and thus
avoids having many unsatisfied external references error messages
reported when either lustre-ldiskfs or zfs-modules RPMs are missing.
Users willing to build Lustre FSs on top of ldiskfs/zfs back-ends
will have to install the corresponding RPM.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Ib406443186026ed5ac3dc7b3ec30db41aedac2a2
Reviewed-on: http://review.whamcloud.com/4869
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Brian J. Murrell <brian.murrell@intel.com>
Reviewed-by: Christopher J. Morrone <chris.morrone.llnl@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>