supporting cassandra authentication

If authentication is enabled in the testbed.py for cassandra, changes have to be made in the provisioning and controller to connect with cassandra

Analaytics, config(api-server, schema-transformer , svc-monitor) and discovery make
connection to cassandra.

Gendb and pycassa are libraries we use to make connection to cassandra.

If authentication is enabled, an api "login()" has to be called in case of gendb, before making other API calls and in the case of python clients a dictionary containing username and password is passed as an additional argument to ConnectionPool api

On the provisioning side, we read the authentication information from the testbed.py and create
a new file called contrail-cassandra.conf. This contains the serverlist, username and password.
The cassadra.yaml file is modified to support password authentication then account is created in cassandra first and the analytics daemons, config and discovery daemons are then passed this config file when invoked.