LU-4276 ldiskfs: enable read/write access by default

LU-4276 ldiskfs: enable read/write access by default

Add build time config option to allow read/write access by default.
While the new CONFIG_LDISKFS_FS_RW only matters in SLES11 builds,
it's easiest to just add the flag to all builds unconditionally.
It will be ignored in builds where it doesn't matter.

Lustre-commit: 14c94c20c3447584e81d720c2b2a17888716709e
Lustre-change: http://review.whamcloud.com/8335

Signed-off-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I4fcf0b2f884b1442db0aac5788bf62f07537c5d4
Reviewed-on: http://review.whamcloud.com/8779
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>