Add integration test for listing role assignments for particular user

[gtema]

The API test for trying to rescope into one of the projects it has access to caught few issues:

• listing role assignments by only a user was mixing up roles assigned to system and project due to the use of HashMap by role_id (it is absolutely normal to have multiple assignments for the same role on different targets)
• corrupted list was returned in the /auth/projects from the api and internal filter (that only lets GroupProject, UserProject assignments) resulted in the empty list
• empty list went into the list of the projects returning all projects
• auth into the scope that the user does not have roles on returns 500

Some of those errors should have been caught already on the integration test:

• assign a user the same role on different projects (including system)
  • list role assignments passing only actor_id
  • list role assignments passing only role_id