E2e image sources hard coded

[lentzi90]

/kind bug

What steps did you take and what happened:

I noticed that we have hard coded a few things with the introduction of ORC in the e2e tests. This unfortunately makes the tests much less flexible than they used to be. In theory, we could point to any OpenStack-based cloud, tune the e2e config to match and run the suite.
The images used could differ.

Now with ORC we have hard coded where the images should come from, while still allowing the exact name to be configurable.
This does not make sense to me. We should make the source also configurable.

I think/hope it is already possible to pre-create the images and ORC will just adopt them. This is good.

What did you expect to happen:

It should be possible to run the e2e test suite in different configurations without assumptions on what exact images would be used or where they can be found.

Anything else you would like to add:

I intend to work on this but I don't have an estimate on when I will have the time.