tools: cpt2 -- Initial commit

Here is an initial commit for cpt2 tool. cpt2 stands for "checkpoint to"
and its main purpose to convert OpenVZ dump files to criu format.

The following entries are were converted in this alfa release
(it's easier to count what is supported rather than missing :)

 - signal handlers
 - task states (gpr,fpu), creds
 - regualr files (including pipes, but without pipe data)
 - tty
 - mount points
 - memory (including vdso)
 - unix/inet/netlink sockets

An easy way to test it (as I did) is to make a suspend under
OpenVZ kernel with vzctl help, then reboot to latest vanilla
kernel (or criu kernel), mount container root filesystem to
some new root, say

	mount --bind /vz/private/101 /vz/root/101/

(don't forget to call for mount --make-rprivate /vz/root/101/
 after). Then run converter, for example

	./cpt2 -v 4 -D test/out/ -f test/101.cpt --root /vz/private/101/

which produce really a *lot* of debug information on your terminal.
And finally run criu restore procedure (after reboot to a proper
kernel of course)

	./criu restore -v 4 -D tools/cpt2/test/out/ --root=/vz/root/101/

In my simple testing case I've got the following process tree after restore

 | 11481 pts/2    S+     0:00  |               \_ ./criu restore -v 4 -D tools/cpt2/test/out/ --root=/vz/root/101/
 | 11485 ?        Ss     0:00  |                   \_ init
 | 11494 ?        Ss     0:00  |                       \_ /sbin/udevd -d
 | 11495 ?        Ss     0:00  |                       \_ /usr/sbin/sshd
 | 11496 ?        Ss     0:00  |                       \_ xinetd -stayalive -pidfile /var/run/xinetd.pid
 | 11497 ?        Ss     0:00  |                       \_ /usr/sbin/saslauthd -m /var/run/saslauthd -a pam -n 2
 | 11507 ?        S      0:00  |                       |   \_ /usr/sbin/saslauthd -m /var/run/saslauthd -a pam -n 2
 | 11498 ?        Ss     0:00  |                       \_ sendmail: accepting connections
 | 11499 ?        Ss     0:00  |                       \_ sendmail: Queue runner@01:00:00 for /var/spool/clientmqueue
 | 11500 ?        S      0:00  |                       \_ /sbin/rsyslogd -i /var/run/syslogd.pid -c 4
 | 11501 ?        S      0:00  |                       \_ /sbin/rsyslogd -i /var/run/syslogd.pid -c 4
 | 11502 ?        S      0:00  |                       \_ /sbin/rsyslogd -i /var/run/syslogd.pid -c 4
 | 11504 ?        Ss     0:00  |                       \_ /usr/sbin/httpd
 | 11509 ?        S      0:00  |                       |   \_ /usr/sbin/httpd
 | 11505 ?        Ss     0:00  |                       \_ crond

And yet don't expect anything magic, it's alfa stage of the tool
which will be heavily lifted, thus no use for anything but
testing purpose.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>