InteractiveClient should timeout/give feedback if the master hostname is not correct

Currently in the client mode we try to connect to port 15140 on vcloud-master.sosy-lab.org ( the client creates ~/.verifiercloud/client/Config with these values by default).

So if someone else wants to run a vcloud-master and they run the client mode, they process will just stall indefinitely, one needs to abort with ctrl+c:

$ java -jar vcloud.jar  client
^C
$

Instead it would be good if the connection attempt times out or fails after x seconds. Alternatively we could just issue a warning on stderr which hints to the option master from the configuration file.