Configure integration tests to use the Eucalyptus release candidate.

Created by: smarnach

This configures the integration tests to use the current Eucalyptus release candidate instead of the Cypress release.

For edx-platform and configuration, custom branches are used with some extra commits on top of the release candidate:

• Additional commits for configuration
• Additional commits for edx-platform

Manual testing isn't necessary for this PR; all we need is the integration tests pass.