LU-1930 build: Back end file system fixes.

LU-1930 build: Back end file system fixes.

Currently Lustre for ZFS requires the zfs development
rpm for its userland support to be installed on the
build machine so we can create the lustre zfs utilities.
What this patch does is allow a user to be able to build
against the zfs/spl source drops as well as the rpms.
A work around is provided so we can point the lustre
build system to were a user can temporary install the
zfs user land headers.

Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I8e5586ed22956a9dd4799826a442b8f5a895d872
Reviewed-on: http://review.whamcloud.com/3980
Reviewed-by: Brian J. Murrell <brian.murrell@intel.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>