mount: simplify devpts_dump

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
mount: parse devpts options

The newinstance options isn't shown in mountinfo. Currently it is
detected in devpts_dump. It is added only for root mounts and it
isn't added for bind-mounts. So mounts_equal(a, b, true) returns false
for such mounts and criu doesn't understand that they should be
bind-mounted.

Reported-by: Tycho Andersen <tycho.andersen@canonical.com>
Cc: Serge Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>