LU-2880 ldiskfs: Added mount option to enable dirdata.

LU-2880 ldiskfs: Added mount option to enable dirdata.

Added the code to set mount option for enabling the dirdata in
osd_mount(). This will set the dirdata option for lustre
filesystems only. The dirdata mount option would be checked in
get_dtype() to decide whether to pass dirdata flag as well while
reading the file type.

Signed-off-by: Manisha Salve <msalve@ddn.com>
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I07f430c5cd7ad92b81746085b05b53c1202dd725
Reviewed-on: http://review.whamcloud.com/6495
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>