Make consistency validation for crdt tests consider failed commands

[volkerstampa]

The crdt-counter-partitions.py indicates a failure when the actual counter value does not match the expected one. The expected one is computed from the inc/dec commands being sent to the applications, however this computation does not consider that these commands can fail (for example when the cassandra nodes are not available)

For this the application must return if a command could be processed successfully or not.