Filter User by project

In version v2.0 keystone allows filtering users by projects (v2.0/tenants/{tenantId}/users) but in v3 it doesn't.

If you need to list the users belonging to a project in keystone v3, you must use the role_assignments API, but it only returns a list of user_ids. To get further information like login and name, it is necessary to perform another query, using this id as a parameter, using the user API.

We create the API call "v3/users?project_id={project_id} ", which will internally make the process above described, returning information from the users, instead of only the user_id.

Implements: blueprint filter-user-by-project-v3
Merge branch 'filter_user_by_project' of https://github.com/raildo/keystone-1 into filter_user_by_project