Stats: Wrong stats shown for .com blog added via self-hosted pathway.

[aerych]

To reproduce:
Be logged into .com and have a .com blog in the app.
Add a new blog to the app. Use the self hosted path way and add a .com blog.
View stats on the first .com blog added the normal way.
Switch to the .com blog you added via the self-hosted path.
Stats still show the first .com blog's stats even after refreshing.

[roundhill]

Also, if you add a WordPress.com blog to the app, then add a Jetpack site that uses the same credentials, the app still prompts you for a login when visiting stats. We should try the global WP.com credentials first, then prompt if they don't work.