LU-15873 osd: heed readonly mount upon osd-ldiskfs device

LU-15873 osd: heed readonly mount upon osd-ldiskfs device

Mount device rdonly for scrub if instructed.

Avoid write FID EA upon rdonly osd device.

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I9d24bdebfa2c6a98dc583760413e957ebcf4bca7
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/48098
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>