* Delete response_topic_prefix
The Response-Infomation in CONNACK was misinterpreated, it should
not be a broker's global config, instead, it should be per-client
or even per-session prefix/suffix mechanism
* Delete request-response code from emqx_client
* Add request-response test code
* meck as default dependency --- temp workaround for dep-vsn-check
spring2maz