cassandra-maven-plugin: CMP-2. Cassandra Maven plugin should enable user to select ports with the Build Helper Maven plugin.

issue: https://jira.kiji.org/browse/CMP-2
review: https://review.kiji.org/r/2042
commit: https://github.com/kijiproject/cassandra-maven-plugin/commit/9022735e5c08ad3d28b879d016905c0a1fc5b6ae