Update Images v2 fixture to allow Preprod setup

*Refactored setup class to allow the use of Preprod configurations
*Changes made are more consistent with how Compute is setup now
*Added summary documentation
*Changed base_url to override_url

Change-Id: Iaa606a5c532bde806d2f698538c293e412437bb4
Merge "Update Images v2 fixture to allow Preprod setup"