ECOM-113: Already verified page sometimes displays the incorrect price

Use new-style course locators consistently when setting the donation amount in the session
Update devstack settings to use new CyberSource API

Turns out this was related to OK.

@dianakhuang @stephensanchez Please review.

[ECOM-113](https://openedx.atlassian.net/browse/ECOM-113): Already verified page sometimes displays the incorrect price