I have added two tests. One checks the usual scenario where the
instance's config specifies a `http_port`. In that case, we expect the
`http_port` to be part of the response. The other scenario checks what
happens when the config doesn't specify a `http_port`. It's hard to
nail down the expectation there without hardcoding the error
response (which is not what we generally want) but I'm mainly checking
that no HTTP port is mentioned. This particular test would have failed
before my previous fix, because the TCP handler wouldn't have managed
to send back an HTTP response and `requests.post` would have thrown an
exception.
