Jetpack Signup Flow pushes 3 buttons instead of present

[mindgraffiti]

After the Jetpack install flow, the user is asked to sign in again. The LoginEmailViewController is presented, and there text and a link below the email field that says, "Don't have an account? Sign up"

Tapping the "Sign up" link pushes the 3 button view instead of presenting the 3 button view. Pushing the nav creates the black screen (seen in Figure 2 below).

Steps to Reproduce

1. Have a self-hosted site that doesn't have Jetpack connected. (This also works if you go to the site, Jetpack > and scroll to the bottom to find the "Disconnect" button and click it.)
2. Log out of the WPiOS app if you are logged in.
3. Log into the app through the self-hosted flow: Login > enter site address text link button
4. After completing the login flow, go to the Notifications tab
5. Follow the Jetpack install flow. Once it is successful, it will ask you to set up Jetpack.
6. The "Set up" Jetpack button should navigate you to the email login screen. (See Figure 1 below)
7. Tap the "Sign up" text link button.
   Expected: the 3 button view appears as an overlay to the email login screen.
   Actual: the 3 button view is pushed and the background is black.

Figure 1

Figure 2

[mindgraffiti]

Closed via #234