block/dirty-bitmaps: prohibit removing readonly bitmaps

Remove is an inherently RW operation, so this will fail anyway, but
we can fail it very quickly instead of trying and failing, so do so.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20190301191545.8728-6-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
1 file changed