fix parse_mnt_flags() to dump/restore STRICTATIME correctly

CRIU always retores the mounts as MNT_RELATIME. This is because the
kernel uses this mode by default, so we need to pass MS_STRICTATIME
explicitely if we didn't see "noatime" or "MS_RELATIME".

While at it, make mnt_opt2flag[] and sb_opt2flag "static", otherwise
gcc actually creates these arrays on stack even if there are "const".

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>