test(auto-rules): Add POST rule itests

[jan-law]

Related #474

Adds integration tests to cover 4xx status codes defined by RulesPostHandler.java.

[jan-law]

Note: When using sendForm() to POST a new rule, Vertx will set the Content-Type header to application/x-www-form-urlencoded, unless you specify multipart/form-data. Any attempts to overwrite the Content-Type with an invalid value will be overridden with application/x-www-form-urlencoded.

void sendForm(MultiMap body,
              Handler<AsyncResult<HttpResponse<T>>> handler)

Like send(Handler) but with an HTTP request body multimap encoded as form and the content type set to application/x-www-form-urlencoded.
When the content type header is previously set to multipart/form-data it will be used instead.

Parameters:
body - the body

However, POSTing a rule with JSON allows me to test invalid mimes, as Vertx won't check the Content-Type header when calling sendJsonObject().

default Future<HttpResponse<T>> sendJsonObject(JsonObject body)

Parameters:
body - the body

[andrewazores]

Looks good otherwise.