CLUSTER-64. Cleanup Dockerfiles, add cdh5.0.4 and cdh5.1.2

issue: https://jira.kiji.org/browse/CLUSTER-64
review: https://review.kiji.org/r/2199
CLUSTER-63. Make bento-cluster installable through pip alone.

issue: https://jira.kiji.org/browse/CLUSTER-63
review: https://review.kiji.org/r/2195