LU-14593 utils: specify libzpool

LU-14593 utils: specify libzpool

otherwise libmount_utils_zfs doesn't build on some platforms

Test-Parameters: trivial
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Id850ba519f7a898e73c099887f0c9eca5c9b5b6f
Reviewed-on: https://review.whamcloud.com/43236
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Oleg Drokin <green@whamcloud.com>