LU-11845 osd-zfs: Support encrypted ZFS datasets

LU-11845 osd-zfs: Support encrypted ZFS datasets

Call zfs::dmu_objset_own and zfs::dmu_objset_disown with
decrypt=B_TRUE

This is called the same way as in zfs modules.

Fixes: 0fedb017c1 ("LU-9890 osd-zfs: dmu_objset_own/disown changes")
Test-Parameters: envdefinitions=ZFS_MKFS_OPTS="encryption=on -o keylocation=file:///etc/adjtime -o keyformat=passphrase" testlist=sanity fstype=zfs
Signed-off-by: Nathaniel Clark <nclark@whamcloud.com>
Change-Id: I1d9bc1a579ac26706a9f6cc5a0d52649ce005228
Reviewed-on: https://review.whamcloud.com/33999
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>