Initial support for single instance Cassandra Database

Reasons
- This code adds ability to create/delete instance
with mongodb service type. No other operations supported.
- Trove should support multiple extensions. One of the is NoSQL support.
Main goal is to add support for Apache Cassandra NoSQL database.

Changes
This code adds ability to create/delete instance
with cassandra service type. No other operations supported.

Change-Id: I67733f0ba18aae513465d66bb48e44bbb316a575
Implements: blueprint cassandra-db-support
Merge branch 'bp/cassandra-single-instance-support'