Rename NIMBUS_IP -> NIMBUS in docs
Rename nimbus_ip -> nimbus in StormCluster
Rename 'storm_cluster_ip' config var to 'nimbus'

Previously, we changed on the CLI option from --storm-cluster to --nimbus
without modifying pyleus.configuration.

This brings in sync the CLI option and config var.

Closes #2
Introduce --nimbus-host/--nimbus-port options

Closes #35
Add tests
Update README.rst and docs
Update docs per review
Merge pull request #36 from patricklucas/add_nimbus_port_option

Add nimbus port option