Use the ZmqClient reqrep pattern rather the local (and wrong) one
Move connection checking into the ZmqClient
Make the ZmqClient more robust to network failures:
 - the reqrep method is correctly synchronized
 - reqrep is only called connected
 - reqrep retries multiple times before giving up
Use absolute timestamp for debug messages and stop the locomotor before
quitting
Made non-blocking / resilient to network failures
Merge branch 'master' of https://github.com/flupes/GrannyRoomba