LU-14696 llite: check read only mount for setquota

LU-14696 llite: check read only mount for setquota

During setting quota, it should fail if the mount is read-only.

Lustre-change: https://review.whamcloud.com/43765
Lustre-commit: 29e00cecc6019fbdb5bd98511970970ac5ef5318

Change-Id: I966ac71d0a4a72dcb998f09ffc0f99ae28498e27
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/46766
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>