Add a Congress driver for Keystone

This driver uses three keystone API calls to populate Congress tables users,
roles, and tenants.  These are the columns for these three tables:

columns ('username', 'name', enabled', 'tenantId', 'id', 'email').
roles ('id', 'name')
tenants ('enabled', 'description', 'name', 'id')

The keystone driver includes a test.

blueprint: refactor-drivers

Change-Id: I8b77576a72e953971bd99bd7cb0a947bf5dc5aa9
Merge "Add a Congress driver for Keystone"