Do not load auth plugins by class in tests

Remove the need for loading auth plugins by class in test cases as
loading auth plugins by class has been deprecated.

Tests that explicitly test loading by class name still exist.

Change-Id: I50a66746ca65a5cfbfadb653bfd9493c415017d5
bp: deprecated-as-of-juno
Merge "Do not load auth plugins by class in tests"