Optimize org channel accessibility query (bsc#1211874)

[nadvornik]

What does this PR change?

This should improve the slow query on channel accessibility by org.
Main changes:

• COUNT replaced with EXISTS
• do not use views
• rhnOrgChannelTreeView uses union of separate SELECTs for parent and child channels. In this case, single SELECT is ok.
• handling of public channel family in rhnOrgChannelFamilyPermissions might be inefficient, not sure

Added unit test to make sure the query behaves the same as before.

GUI diff

No difference.

• DONE

Documentation

• No documentation needed: only internal and user invisible changes

• DONE

Test coverage

• Unit tests were added

• DONE

Links

Might fix https://bugzilla.suse.com/show_bug.cgi?id=1211874

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[github-actions]

Suggested tests to cover this Pull Request

[rjmateus]

I think this can be provided to the customer as PTF. The implementation looks good, but since we have a customer to test it, it would give us good feedback.

[lucidd]

looks good just a clarification. I assume the test was run before and after the change and behaved the same right?

[nadvornik]

I assume the test was run before and after the change and behaved the same right?

yes