Fix login/logout/login form error states

@tilgovi this is one potential fix for the issue you raised on #1275. There are two issues currently with this.

1) I have a failing test, I can't seem to get the test to pass, it's setting up the correct state and performing the same actions as the login flow but for some reason it's not passing. Any ideas?
2) This whole error validation is falling into serious hack territory and indicates that we need to take a step back and look at how we wire up our forms across login and account management otherwise this is just going to be a persistent pain point.

https://github.com/hypothesis/h/pull/1275#issuecomment-51777983