Making contrail config services read multiple config files if provided.

contrail config services such as contrail-api, contrail-schema, contrail-svc-monitor reads
authentication details from one config file. We currently populate the authentication
section [keystone] in their irespective config file say contrail-api.conf, schema_transformer.conf etc.

Modified them to take multiple --conf_file option and read all of them, This way we can skip
auth config in the config services in case of deployment scenarios where openstack is not the orchestrator.

Change-Id: Ib26841e32320cfff1df98723d186700f88b4f1f0
Partial-Bug: 1378497