Use infra mirrors for advanced image prepare

In CI we seeing issues like [1] randomly while Customizing
test image. Let's use infra mirrors instead of ubuntu
public mirrors.
Added conditions so the override apply only when ubuntu images and nodes
involved.

[1] File has unexpected size (2351988 != 2352236).
    Mirror sync in progress? [IP: 91.189.91.81 80]

Related-Bug: #2110191
Change-Id: I8c528791e7c08a92302dfe7c8c4963b6e1d983bd
1 file changed