LU-5822 osd-ldiskfs: Correctly return OS_STATE_READONLY

LU-5822 osd-ldiskfs: Correctly return OS_STATE_READONLY

Ensure that read-only devices correctly return their state so that
the health_check file will be accurate

Signed-off-by: Matt Ezell <ezellma@ornl.gov>
Change-Id: Iea38c924ca0d8cb543b77599019fc88fd8b58105
Reviewed-on: http://review.whamcloud.com/12463
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>