LU-7534 build: Allow lustre to build against ZFS/SPL DKMS install

LU-7534 build: Allow lustre to build against ZFS/SPL DKMS install

The current method to build against DKMS installs of ZFS and SPL
assumes directories like this:

  /var/lib/dkms/spl/${VERSION}/build
  /var/lib/dkms/zfs/${VERSION}/build

Unfortunately, that "build" directory was really just a temporary
step in the DKMS build process.  Older versions of DKMS forgot to
clean up that directory, but in RHEL7 at least, DKMS no longer
leaves that aroudn.

Instead we need to look in these places for source code:

  /var/lib/dkms/spl/${VERSION}/source
  /var/lib/dkms/zfs/${VERSION}/source

and in these places for the per-kernel object info:

  /var/lib/dkms/spl/${VERSION}/${LINUXRELEASE}/${target_cpu}
  /var/lib/dkms/zfs/${VERSION}/${LINUXRELEASE}/${target_cpu}

The changes in this patch update the Lustre build system to
look in those corrected directories for DKMS builds of SPL
and ZFS.

Change-Id: I614b5fc6a6a506cb3f927b2c39ce27160979aaf7
Signed-off-by: Christopher J. Morrone <morrone2@llnl.gov>
Reviewed-on: http://review.whamcloud.com/17536
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>