Local scoping and local tempdirs for edge case test file

[slager]

This test file created and sometimes deleted numerous test data packages in temporary directories, and had 300+ lines of test code all scoped inside the same testthat block. As such, it was confusing to follow and maybe prone to some hard-to-notice test inter-dependencies.

This PR splits up those tests into 11 different blocks, each with locally scoped variables and locally scoped auto-deleting temporary directories. This was needed prep for some upcoming refactoring I wanted to do, and will be useful for eventual re-organizing of the test files. There's still room to improve these tests, which didn't have many code comments.

This PR also renames config.yml to datapackager.yml in the documentation (inspired by finding an old instance of that filename lingering in the test code itself).