LU-169 lov: add basic infrastructure for layout lock

LU-169 lov: add basic infrastructure for layout lock

This patch adds some basic infrastructure to support the layout lock
in a near future. This includes defining a new inode lock bit to lock
the file layout (namely MDS_INODELOCK_LAYOUT) as well as a new lookup
intent (IT_LAYOUT).

Signed-off-by: Jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Change-Id: Ibf1c3c166b5def4654684febbcf3a99ea7e482eb
Signed-off-by: Johann Lombardi <johann@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1854
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>