Import: Pass "engine" and "from_site" to new user endpoint

[jonathansadowski]

Changes proposed in this Pull Request

This PR passes the "engine" and "from_site" to the new user endpoint, which allows us to continue the import flow after email confirmation.

Testing instructions

• Apply changes from D19275-code and D19384-code and follow the associated test plans (make sure appropriate sites are sandboxed).
• Open the network inspector to capture the request to the new user endpoint (filter for "new")
• Browse to http://calypso.localhost:3000/start/import
• Enter a known valid wix site to import
• Submit the form
• Complete the signup
• Verify that import_engine and import_site are correctly populated and sent to the new user endpoint via the network inspector

Addition testing that should pass if both D19275-code and D19384-code are applied:

• Click the confirmation link you receive via email
• Verify that you're redirected to the import flow and shown a preview of your site.

[matticbot]

Test live: https://calypso.live/?branch=update/import-account-creation

[ghost]

That's a great PR description, thank you so much for your effort!

Generated by 🚫 dangerJS

[jblz]

I hit a reference error when I went through a logged out flow with this on the last screen, but it "worked" (created the user w/ attrs, site, etc).

Looking to see if it's in master as well.

[jblz]

Looks like that bug is in master, so this is a 👍 from me and I'll chase that bug in another PR.

[jonathansadowski]

Thanks for the review, and thanks for chasing that bug down.

[jblz]

I'm pretty sure my error was because of something broken on my sandbox. Can no longer reproduce.