phaul: Prepare a socket for memory migration

Currently on each iteration page server opens a
listening socket and criu pre-dump/dump connects
to it.

This is wrong, criu should accept an FD to xfer
memory through from p.haul. To make this happen
p.haul must be able to establish a side channel
and this patch does so.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
criu: Use swrk instead of remote service

The plan is to push page server socket to criu from
p.haul. This can be done by passing one with scm_rights,
but python2.2 cannot do it easily. Thus, for now, we
end up spawning the swrk, it will inherit all the fds
and we'll just "tell" one where the socket is.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
criu: Put the mem_sk socket into dump and page server

This will allow criu not to assign new port on every iteration,
not to issue the connect on every iteration and to use custom
file descriptor for it.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
phaul: Put a number in log file names

This will allow to split page-server and pre-dump logs
from different iterations.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>