staging/lustre/hsm: Add hsm_release feature.

HSM Release is one of the key feature of HSM. To perform HSM
release, clients need to acquire the file lease exclusivelt and
flush dirty cache from clients. A special close REQ will be sent
to the MDT to release the lease and get rid of OST objects.

Lustre-change: http://review.whamcloud.com/7028
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-1333
Signed-off-by: Aurelien Degremont <aurelien.degremont@cea.fr>
Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Signed-off-by: Peng Tao <bergwolf@gmail.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>