Add new test for RAPI

Unlike existing tests, this actually tests RAPI at the interface with
the HTTP server. This way authentification can also be tested. A test
for “/2/query/…” is included as it's a bit special.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Bernardo Dal Seno <bdalseno@google.com>