Remove "booted" step from Smokey

Our application workers run all the time, and don't need to be booted
with a HEAD request.
Add deprecation message to admin uploader tests
Add Signon redirect test for new admin app

The new admin app should redirect to Signon when you hit the /login
page.
Add admin app Signon integration test

This commit also makes the Signon step a bit more general, so that
we can use it for both the admin features we currently have.
Merge pull request #27 from alphagov/add-admin-app-tests

Add new admin app tests