Make requests to UAA about users more intelligently

This very simple change prevents us from making a request with an empty
filter that might return all of the users in the space.

[Finishes #70051880, 70130480]
Start removing more global state

It's been more than a little disappointing that we've had assertions in
our tests that rely on a global bool in a testhelper package. Changing
this for one test now so that we have a pattern to abide by later. My
hope is that we can root out the rest of these one by one.

[Finishes #68922816]