ext4: return EROFS if device is r/o and journal replay is needed

commit 4753d8a24d4588657bc0a4cd66d4e282dff15c8c upstream.

If the file system requires journal recovery, and the device is
read-ony, return EROFS to the mount system call.  This allows xfstests
generic/050 to pass.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Willy Tarreau <w@1wt.eu>