Document and ensure legacy HostingServiceClient.json_*() result types.
Review Request #11645 — Created June 3, 2021 and submitted
This updates the documentation for the
json_delete()) to specifically
say that header keys/values are native strings.
It also adds unit tests that guarantee this as well. While here, some
issues with existing unit tests were also fixed.
This will help with ensuring proper usage without any confusion over
Unit tests passed on Python 2 and 3.