ext2: change the default behaviour on error

ext2 file system was by default ignoring errors and continuing.  This is
not a good default as continuing on error could lead to file system
corruption.  Change the default to mark the file system readonly.  Debian
and ubuntu already does this as the default in their fstab.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: <linux-ext4@vger.kernel.org>
Cc: Eric Sandeen <sandeen@redhat.com>
Cc: Jan Kara <jack@ucw.cz>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>