Implement a __contains__ override for extension manager

Change-Id: I027c576e36fc0f4e016b6aec67f585bf2c03bd7b
Closes-Bug: #1374099
Workflow documentation is now in infra-manual

Replace URLs for workflow documentation to appropriate parts of the
OpenStack Project Infrastructure Manual.

Change-Id: I5637374ac8b957e948c2345a883636198cf15e9b
Merge "Implement a __contains__ override for extension manager"