ORNL-3 mntopt: consider low-layer options for MDT ACL flags

ORNL-3 mntopt: consider low-layer options for MDT ACL flags

Currently, MDT layer enables ACL support by default without checking
whether low-layer (ldiskfs) enables ACL support or not, then causes
unnecessary data traffic on network and through MDS stack for ACL.

So MDT should communicate with low-layer before setting ACL flags.

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Change-Id: I804f10bf486745ddd3b23b89e959dfd585589ac0
Reviewed-on: http://review.whamcloud.com/1211
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>