certificate/keystore generation script
cassandra-ca-mgr accepts a yaml-formatted manifest file as its only argument
and generates a root CA and corresponding Java truststore, and an arbitrary
number of Java keystores, signed by the root CA.
The script is idempotent, so subsequent invocations with an identical
manifest should effect no change; Invocations with additional keystore entity
definitions will result only on the creation of the new keystores.
Try `pydoc ./cassandra-ca-mgr' to see an example of how to format a manifest.