clueanup

I understand @Danny-Hazelcast objections against passing behaviour flag (+Hazelcast instance!) to what's supposed to be a small utility method. I don't like doing if / else branching in each test either. 

Perhaps we shouldn't use raw StringUtils to generate keys? It's supposed to create Strings and not keys after all. In order to move forward I'm suggesting these steps:
* Remove the change related to key generating from this PR so it can be merged ASAP
* Create a new PR for the key issue. I suggest having an inteface KeyGenerator with 2 implementations. One impl will generate randomly distributed keys, the other one will generate keys not owned by a particular instance. 

It will serve as a strategy to generate keys. If you have different requirements for keys in a future you can easily create a different implementation and add it to different tests easily w/o too many changes. 
This is the idea:
```
public interface KeyGenerator<T> {
    T newKey();
    T newKey(int size);
}

public class RandomKeyGenerator implements KeyGenerator<String> {
    @Override
    public String newKey() {
        throw new UnsupportedOperationException("Not implemented yet");
    }

    @Override
    public String newKey(int size) {
        throw new UnsupportedOperationException("Not implemented yet");
    }
}

public class RemoteKeyGenerator implements KeyGenerator<String> {
    private final HazelcastInstance hazelcastInstance;

    public RemoteKeyGenerator(HazelcastInstance hazelcastInstance) {
        this.hazelcastInstance = hazelcastInstance;
    }

    @Override
    public String newKey() {
        throw new UnsupportedOperationException("Not implemented yet");
    }

    @Override
    public String newKey(int size) {
        throw new UnsupportedOperationException("Not implemented yet");
    }
}
```