Logging in from MyUSA marketing page redirects to app #352
Logging in from MyUSA marketing page redirects to app #352

Tests session is destroyed unless during redirect
Explicitly pass flag to login flow to indicate whether we should redirect back

If the user abandoned the login flow, we do not want to use that return_to path later. So, unless a flag is explictly passed to the login flow, we should clear the return_to.
clean up calls to clear_return_to
Merge pull request #374 from 18F/feature/login_redirect

Feature/login redirect