RPC: add script to test the new RPC version interface

This script connects to 'criu swrk' and asks for the version. If running
from a git checkout the output would look like this:

 $ ./version.py
 Connecting to CRIU in swrk mode to check the version:
 RPC: Success
 CRIU major 2
 CRIU minor 12
 CRIU gitid v2.12-635-g6d3ae4d

If not running from git checkout it looks like this:

 $ ./version.py
 Connecting to CRIU in swrk mode to check the version:
 RPC: Success
 CRIU major 2
 CRIU minor 12

If running with a CRIU binary which does not support the VERSION
command:

 $ ./version.py
 Connecting to CRIU in swrk mode to check the version:
 Error (cr-service.c:116): RPC error: Invalid req: Success
 RPC: Unexpected msg type

Signed-off-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>