added IP_PREFIX

* used to easily set the ipspace of the test-cassandra-cluster
* switched the addresses from 127.0.0.? to 127.0.1.? to prevent collisions with an already running cassandra instance
* added "ip" as options for the stress-example, 127.0.0.1 is the default
* added -Dipprefix= to maven options
Merge pull request #27 from damoon/ipprefix

testnodes should move from 127.0.0.n to 127.0.1.n