Groups and Roles support

build status https://travis-ci.org/msumit/qds-sdk-py
Can these policies be more complicated JSON?

Should we add an option to read them from a file? (Just like we do currently for customer-ssh-key etc. [qds_sdk/cluster.py#L260](https://github.com/qubole/qds-sdk-py/blob/452e638f365760f4bdba864af53ee7afad93245a/qds_sdk/cluster.py#L260))