CLUSTER-57. Use docker tags to allow platform version specification

issue: https://jira.kiji.org/browse/CLUSTER-57
review: https://review.kiji.org/r/2170
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
CLUSTER-65. Zookeeper quorum string written to hbase-site.xml incorrectly includes a port.

issue: https://jira.kiji.org/browse/CLUSTER-65
review: https://review.kiji.org/r/2228
CLUSTER-72. When using bento-cluster on mac systems, --docker-address must be specified explicitly.

issue: https://jira.kiji.org/browse/CLUSTER-72
review: https://review.kiji.org/r/2239
CLUSTER-66. Separate hosts file write into a separate script that can be executed as root.

issue: https://jira.kiji.org/browse/CLUSTER-66
review: https://review.kiji.org/r/2240
CLUSTER-73. Add 'robertchu' to the reviewers file for bento-cluster.

issue: https://jira.kiji.org/browse/CLUSTER-73
review: https://review.kiji.org/r/2241
CLUSTER-75. Remove leftover dead code.

issue: https://jira.kiji.org/browse/CLUSTER-75
review: https://review.kiji.org/r/2247
CLUSTER-79. Add error checking/debug bash lines to the dev bento-env.sh script.

issue: https://jira.kiji.org/browse/CLUSTER-79
review: https://review.kiji.org/r/2249
CLUSTER-66. Separate hosts file write into a separate script that can be executed as root.

issue: https://jira.kiji.org/browse/CLUSTER-66
review: https://review.kiji.org/r/2250
CLUSTER-80. 'bento start' fails when using a non-interactive shell.

issue: https://jira.kiji.org/browse/CLUSTER-80
review: https://review.kiji.org/r/2251