This is easier to understand: code 0 means no errors.

Reuse the existing test code for the HTTP API - now there is a
'protocol' option per test group, that can be 'http' or 'cli'.

The query documents are generated for the HTTP API.
There is an option to avoid this, but it would complicate the tests.

This way it is easier to control the error messages,
and to print out additional hints.
There is a plan to add more usage information in a new PR.