Signup: Free trials: Only show free trials on signup in the dev environment

[scruffian]

This enables free trials in signup in dev.

Fixes #1417

Testing

1. git checkout update/1417-free-trials-in-signup
2. Open http://calypso.localhost:3000/start incognito
3. Assert that you are show the "Start free trial" button.

• Code review
• QA review

[ghost]

Trial adds a year long subscription instead of just 14/17 days.

[fabianapsimoes]

A few issues related to problems in this flow, just so we make sure to close them before merging this:

• Signup: Checkout sidebar #900 - the confirmation notice overlaps with the sidebar
• Free Trials: Implement free trial hub #1151 - /plans has no indication a free trial is active
• Free Trials: Disable Google Apps for sites with a free trial #1372 - it's possible to get Google Apps with a trial domain

[fabianapsimoes]

Trial adds a year long subscription instead of just 14/17 days.

Just adding that this seems to happen in all cases of trial signup: from /start with a new account, from /start for an existing account, and from /plans for an existing site. We're testing this proxied and unsandboxed.

[fabianapsimoes]

We tested this a bit more:

• not proxied, not sandboxed: no free trial flow, you see the credit card form (which is expected).
• proxied, not sandboxed: free trial flow, but full subscription instead of a 14-day one.
• proxied, sandboxed: free trial flow, and a 14-day subscription (which is how it should work).

[scruffian]

This patch should fix those issues: pb-10333

[ghost]

Works from the scruffian sandbox - 👍

[drewblaisdell]

👍