Speed up tests which are using many container images

[psss]

Several tests failed because of maximum time exceeded after adding an additional image in:

• #4272

Namely these were the affected tests:

• /tests/finish/ansible
• /tests/prepare/ansible
• /tests/prepare/install

Let's investigate ways how to speed up execution of these. We could consider splitting some tests or dropping some combinations.

[happz]

It would be wise to look into what the tests are doing: one of the purposes of the test images is to provide precached metadata for package managers. If this does not work, and package managers fetch new metadata in every test case, it would easily extend the duration of tests.

[psss]

The caching seems to be working fine:

• first test /tests/finish/ansible prepares images in 8 minutes
• second test /tests/prepare/ansible goes through the setup in 6 seconds

It's just that we exercise too many combinations. For example, I'm not sure that we really need to verify that recommend or exclude works across all fedora versions.