LU-3811 hsm: handle file ownership and timestamps

LU-3811 hsm: handle file ownership and timestamps

In hsm_init_ucred() set the capability mask to CFS_CAP_FS_MASK thereby
allowing the coordinator to swap layouts of files not owned by
root. In mdt_orphan_open() raise CFS_CAP_DAC_OVERRIDE before creating
the orphan filee in the MDT's local root. In mdt_hsm_release() set
inode size and timestamps before getting the LOV xattr and ensure that
the orphan file is created with the same UID and GID of the original.
In lhsmtool_posix.c similalrly ensure that the volatile file used for
restore has the same ownership, access and modification timestamps as
the original.

Strengthen sanity-hsm test 24 to check that none of archive, release,
or restore will change the access or modified timestamps. Add 24b to
check that root can archive, release, and restore an ordinary user's
files and that the user will be able to read a released file even if
the parent directory is unwritable.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Id08429cbfed1bbab719f52ed101e61d5e629ccd2
Reviewed-on: http://review.whamcloud.com/7461
Reviewed-by: Aurelien Degremont <aurelien.degremont@cea.fr>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>