LU-1876 hsm: layout lock implementation on server side

LU-1876 hsm: layout lock implementation on server side

* enabled OBD_CONNECT_LAYOUTLOCK both on client and mdt
* mdt_object_lock_try() is implemented to try layout lock
* dlm flag LDLM_FL_BLOCK_NOWAIT is added to implement nonblock mode
  dlm lock enqueue
* try layout lock for IT_GETATTR and IT_OPEN
* make layout lock work
* add layout intent support.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I84a6dfca83ded2344240fa5430c9922b7cfc7bcf
Reviewed-on: http://review.whamcloud.com/4417
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Reviewed-by: Oleg Drokin <green@whamcloud.com>