autofs: parse fsinfo stage introduced

Autofs uses packetized pipe (with O_DIRECT), migration of which is not
supported.
Luckely, because we support only empty autofs pipes, they can be collected
into some list and then explicitly treated as normal pipes on dump.

Note: packetized mode is set by kernel inself on mount operation. So, we don't
need to carry the flag at all.

Signed-off-by: Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>