Fixed failing tests in OBS build

[lslezak]

Problem

• Jenkins failed with Release file /etc/os-release not found error
• https://ci.opensuse.org/view/Yast/job/yast-yast-migration-sle-master/1/console

Solution

• Fixed unit tests
• Additionally added mock for obtaining the registration URL which runs a SLP server scan, that's not nice to run for real in the tests

Notes

• No version bump as the package was not released yet (failed in Jenkins)

[yast-bot]

✔️ Public Jenkins job #2 successfully finished
✔️ Created OBS submit request #965419

[coveralls]

Pull Request Test Coverage Report for Build 2052740692

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 69.281%

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Totals
Change from base Build 2051048093:	0.0%
Covered Lines:	106
Relevant Lines:	153

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💛 - Coveralls