btrfs replace on readonly fs should not be allowed.
Regression test case for commit:
bbb651e Btrfs: don't allow the replace procedure on read only filesystems
Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>