Allow installing with existing volumes

[aaannz]

What does this PR change?

This PR add check for existing uyuni-server service and if exists, refuse installation. It also add check for existing volume and display warning that not all installation options are preserved and make sure correct passwords are used.

At the end this PR adds new API call to try to verify if existing organization from pre existing volumes matches what would be created.

One small unrelated change is to use directly SUSEConnect instead of transactional-update --register. For plain status check, which is r/o operation, calling directly SUSEConnect is fine and we don't spend unnecessary time creating and discarding snapshots.

Test coverage

• No tests: add explanation

• No tests: already covered

• Unit tests were added

• [ ] DONE

Links

Issue(s): https://github.com/uyuni-project/uyuni-tools/issues/347

• [X] DONE

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[aaannz]

Adapted:

• now we check for .MANAGER_SETUP_COMPLETE once container startup and issue warning if it is detected.
• check for existing organization now tries to distinguish between connection fail and some unknown failure - these will print error. If auth failure or mistyped org name is detected, only warning is issued, but we continue with success. And lastly if all matches, we just print info about it.