LU-10536 build: add path for libnvpair to zfslib

LU-10536 build: add path for libnvpair to zfslib

For the case of building lustre against the ZFS source tree
instead of an ZFS installation on the node we need to add
the path $zfssrc/lib/libnvpair/.libs so mount.lustre can
link to the library.

Test-Parameters: trivial

Change-Id: Id08cc3aed1bc201611fb9382d2f53e40e69f9544
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/31128
Tested-by: Jenkins
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>