Improve the InfluxDB through-put performance

This changes the current use of the InfluxDB client to instead use a
baked-in client that uses the fasthttp library.

This allows for significantly smaller allocations, the re-use of http
body buffers, and the re-use of the actual bytes of the line-protocol
metric representations.

plugins/inputs/http_listener/http_listener.go

@@ -300,6 +300,9 @@ func (h *HTTPListener) serveWrite(res http.ResponseWriter, req *http.Request) {
 }
 
 func (h *HTTPListener) parse(b []byte, t time.Time) error {
+	if !bytes.HasSuffix(b, []byte("\n")) {
+		b = append(b, '\n')
+	}
 	metrics, err := h.parser.ParseWithDefaultTime(b, t)
 
 	for _, m := range metrics {