LU-4002 hsm: avoid layout lock on unlink and rename onto

LU-4002 hsm: avoid layout lock on unlink and rename onto

In mdt_reint_unlink() and mdt_reint_rename() do not take a FULL inode
lock on the file to be unlinked or the rename target. This avoids a
potential deadlock when unlinking a file under HSM restore.

Signed-off-by: John L. Hammond <johnlockwoodhammond@gmail.com>
Change-Id: Id6b11b9f5c1433221670d154d65d9cec30e260af
Reviewed-on: http://review.whamcloud.com/7792
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>