Explicit reset

Author: pablomartinezbernardo

src/datadog/telemetry/telemetry_impl.cpp

@@ -234,6 +234,7 @@ Telemetry::~Telemetry() {
     // final metric values.
     send_telemetry("app-closing", app_closing());
     http_client_->drain(clock_().tick + 2s);
+    http_client_.reset();
   }
 }