Ensure directory exists before writing systemid

[denyskon]

What does this PR change?

Ensure the directory /etc/sysconfig/rhn exists in proxy-httpd container before writing into it from the uyuni-config.py script. Prevents a crash on init of the proxy-httpd container due to missing directory.

GUI diff

No difference.

Documentation

• No documentation needed: only internal and user invisible changes

Test coverage

• No tests: modifies the init script for the proxy-httpd container to fix a failure, no new functionality

Changelogs

Make sure the changelogs entries you are adding are compliant with https://github.com/uyuni-project/uyuni/wiki/Contributing#changelogs and https://github.com/uyuni-project/uyuni/wiki/Contributing#uyuni-projectuyuni-repository

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Re-run a test

If you need to re-run a test, please mark the related checkbox, it will be unchecked automatically once it has re-run:

• Re-run test "changelog_test"
• Re-run test "backend_unittests_pgsql"
• Re-run test "java_pgsql_tests"
• Re-run test "schema_migration_test_pgsql"
• Re-run test "susemanager_unittests"
• Re-run test "frontend_checks"
• Re-run test "spacecmd_unittests"

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[aaannz]

Thank you for the contribution.

Can you adjust the changelog so it is wrapped at line length 67 characters? See the failed changelog test.

[m-czernek]

Can you also squash the commits please - ideally squash the 5 of your commits into one, and leave the black formatting commit from me separate.

After that, we should be good to merge.