Add option to allow encrypting of sstables.
I have a version of this functionality built on cassandra 2.0 that piggy-backs on the existing sstable compression functionality and ICompressor interface (similar in nature to what DataStax Enterprise does). However, if we're adding the feature to the main OSS product, I'm not sure if we want to use the pluggable compression framework or if it's worth investigating a different path. I think there's a lot of upside in reusing the sstable compression scheme, but perhaps add a new component in cqlsh for table encryption and a corresponding field in CFMD.
Encryption configuration in the yaml can use the same mechanism as
CASSANDRA-6018 (which is currently pending internal review).