Chronograf: Expired auth should navigate user to /login

[jaredscheib]

Expired auth is failing to forcibly navigate user to /login.

This seems due to the fact that a different router is currently returned depending on the App container's this.state.loggedIn bool. When that state changes, it's intended to navigate the user to /login, but instead fails with the error that we cannot change <Router routes>:

This is related to https://github.com/influxdata/chronograf/issues/1095.

[gunnaraasen]

We should also provide a notification to the user on the /login page that their auth has expired.

[goller]

@gunnaraasen, @jaredscheib and I were talking about how to be more informative to the user when expiration occurs. We were discussing if the server's router should redirect to /login or if the react router should.

The current plan is that the react router will handle the redirect _because_ it gives the front-end opportunity to display good messaging as you ask for above.

[jaredscheib]

Agreed, @gunnaraasen and @goller!