ARGO-322:  shore up unit tests for User class

- fix test title for remoteuser tests
- add tests for DOR-wide manager workgroups
- add tests for deprecated DOR-wide (admin, manager, viewer) workgroup names
- add tests for impersonation functionality
- minor formatting fixes (whitespace and indentation)
added back something that i'd previously thought was extraneous
ARGO-322: test is_admin/is_manager/is_viewer in conjunction with impersonation