[master] Fix granting of privileges on Postgres functions

[elpavel]

What does this PR do?

The Postgres module code for granting privileges on functions has issues.
This PR adds a test for grants on Postgres functions, and fixes the issue.
It also fixes a minor issue in revoking privileges on tables.

Previous Behavior

Granting a privilege on ALL functions would run

GRANT EXECUTE ON FUNCTION ALL TO "user"

Revoking a privilege from a table would run

REVOKE SELECT ON TABLE public.badly-named-table FROM ...

New Behavior

GRANT EXECUTE ON ALL FUNCTIONS TO "user"

REVOKE SELECT ON TABLE public."badly-named-table" FROM ...

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs - no change required
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

No

Please review Salt's Contributing Guide for best practices.

See GitHub's page on GPG signing for more information about signing commits with GPG.

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[welcome]

Congratulations on your first PR being merged! 🎉