static: Don't use single sign-in if user explicitly logged out

When the user explicitly logged out, don't try and use single
sign in to authenticate. Otherwise the user would just be logged
in again.

There are two use cases here:

 * The user wants to finish the session and log out
 * The user wants to log in as someone else

So we force display of the login form in the case where logout
was explicitly used.
test: Check negotiate authentication
test: Add some more test dependency lines