preparing for v2.1

* Added `attributes/version.rb` for v2.1 cookbook attributes change
* Added logback attributes and config files for v2.1
* Disabled `log4j-server.properties` for v2.1
* Added v2.1 new parameters to `cassandra.yaml` 
* Disabled old incompatible v2.1 `cassandra.yaml` parameters
* Added `node[:cassandra][:jamm_version]` attribute for `cassandra-env.sh` jamm lib
* Disabled `node[:cassandra][:setup_jna]` for v2.1, jna lib is part of C* package now

Tested v2.1 tarball setup and upgrade from v2.0.8. Hopefully commit will work for dsc21/dsc20.