LU-1548 osd: move i_htree_lock to iam container

LU-1548 osd: move i_htree_lock to iam container

Move i_tree_lock from ldiskfs_inode to iam_container,
so to reduce ldiskfs_inode_info size.

Signed-off-by: wang di <di.wang@whamcloud.com>
Change-Id: I4277e73347380bcb3fd34e3d76f66b1d6ec881f5
Reviewed-on: http://review.whamcloud.com/3561
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/4515
Reviewed-by: Bob Glossman <bob.glossman@intel.com>