The list of users assigned to a project becomes invisible when a domain context
is set in Horizon. If a domain context is set, the user list call should
provide a list of users within the specified domain context, rather than users
within the user's own domain.
Groups tab of project also has the same problem.
Change-Id: Ia778317acc41fe589765e6cd04c7fe8cad2360ab
Closes-Bug: #2054799