[2.0b5] CI - After changing proxy, MAAS cannot install images

[Andres Rodriguez]

After the recent change of image default mirror, I noticed that the CI started failing. After looking into it, I noticed that the images page showed:

"Error: No boot sources provide Ubuntu images."

I initially figured this was because we are in a completely offline environment, and we have no access to images.maas.io. Later, however, when MAAS now has access to the internet via the Proxy, it still shows the same thing.

What the CI is doing:

1. Change the proxy setting with an external proxy.
2. Tell MAAS to import the images (which actually never happens. Image page shows "Error: No boot sources provide Ubuntu images.").
3. Check for imported images - fails.

What I did to fix this:

1. [CI] Change the proxy setting with an external proxy.
2. [CI] Attempt to import the images.
3. [me] Go to settings page, to the Ephemeral Images and clicked "Save"
4. [me] Go to image listing page, images are now available. Start import manually.
5. [CI] Check for imported images - succeeds, and tests finish successfully.