Add more unit test coverage for "copy-pastable" code

[jeroenheijmans]

A bunch of people have started using this repo as a starting point. They might even copy/paste pieces into production applications. Especially these seem important:

• auth.service.ts and notably logic from the constructor, runInitialLoginSequence, canActivateProtectedRoutes$, and login/logout
• auth-guard.service.ts
• auth-guard-with-forced-login.service.ts

There's been only a handful of specs for the auth service ever since a community member contributed them. But it might be good to create this into production-worthy test coverage.

See also #98 (I realized this was an issue while fixing that one).