Switch to SLE15-SP2 base images and change references to v5

[dirkmueller]

Why is this PR needed?

Does it fix an issue? addresses a business case?

add a description and link to the issue if one exists.

Fixes #

Reminder: Add the "fixes bsc#XXXX" to the title of the commit so that it will
appear in the changelog.

What does this PR do?

please include a brief "management" technical overview (details are in the code)

Anything else a reviewer needs to know?

Special test cases, manual steps, links to resources or anything else that could be helpful to the reviewer.

Merge restrictions

(Please do not edit this)

We are in v4-maintenance phase, so we will restrict what can be merged to prevent unexpected surprises:

What can be merged (merge criteria):
    2 approvals:
        1 developer: code is fine
        1 QA: QA is fine
    there is a PR for updating documentation (or a statement that this is not needed)

[jenting]

nit

Suggested change

	command: ['/bin/sh', '-c', 'sleep 3600']"""
	command: ['/bin/sh', '-c', 'sleep 3600']
	"""

[dirkmueller]

It is changing how it was done before. I personally don't really care either way, but I need to update commit message, or create a separate PR for it, or convince that the end-of-file style with newline is better in some regard.

I have very little energy for this.

[jordimassaguerpla]

@jenting This was rebased. If you could review it again, then Dirk could merge it and we will include this in the skuba package for RC1.