onLoginFinished sometimes returns successful == false

[oottinger]

We're having issues using the login code with 2.0.0-RC3 where we occasionally get successful == false in the callback. The authentication worked on the Evernote activity, and when the result gets passed back to our activity, it's inconsistent whether we get a success or failure.

This problem seems to occur a lot more when we use an emulator vs a physical device; and are able to reproduce this in the demo app.

The simplest way to reproduce is to run the demo app in an emulator, and then repeatedly login and logout. You'll notice that sometimes the Evernote authentication activity succeeded, but the returning result in login activity won't trigger the callback successfully.