[CRIU] [RFC] run each test case also in --check-only mode

[Adrian Reber]

The following patch tries to add the --check-only option to each test case.

For each test case now the following step are run:

 * dump in --check-only mode
 * real dump
 * restore in --check-only mode
 * real restore

For most test cases this works successfully. Unfortunately not for network
test cases. There are multiple problems:

./zdtm.py run -f h -t zdtm/static/socket-tcp --check-only

=== Run 1/1 ================ zdtm/static/socket-tcp

======================= Run zdtm/static/socket-tcp in h ========================
Start test
./socket-tcp --pidfile=socket-tcp.pid --outfile=socket-tcp.out
Run criu dump in check-only mode
Only checking if requested operation will succeed
Run criu dump
Run criu restore in check-only mode
Only checking if requested operation will succeed
Checking mode enabled
Run criu restore
=[log]=> dump/zdtm/static/socket-tcp/31/1/restore.log
------------------------ grep Error ------------------------
(00.008036) Error (criu/util.c:707): exited, status=1
(00.008050) Error (criu/netfilter.c:91): Iptables configuration failed
(00.009993) Error (criu/util.c:707): exited, status=1
(00.010007) Error (criu/netfilter.c:91): Iptables configuration failed
------------------------ ERROR OVER ------------------------
Send the 15 signal to  31
Wait for zdtm/static/socket-tcp(31) to die for 0.100000
############### Test zdtm/static/socket-tcp FAIL at result check ###############
Test output: ================================
11:30:41.072:    31: ERR: socket-tcp.c:190: can't write (errno = 104 (Connection reset by peer))

 <<< ================================
##################################### FAIL #####################################

The first problem is that the network unlocking fails for the real restore.
The '--check-only' restore already unlocked the network. Which is wrong, but
I am not sure what the right solution is. Should I just ignore network
unlocking in check-only mode?

The second problem seems to be that when CRIU restores the process in
real restore mode the sockets cannot be restored again and I am not sure
why.

So I am asking for some help how to correctly handle the network in
--check-only mode:
 * What should be done with the unlocking? Just skip it? Can it be simulated?
 * What should be done with the sockets? How much can be simulated during
   socket restore? Should it just be skipped completely?

		Adrian