Merge branch 'update/qemu_test_IDFv4.3' into 'master'

CI: Update QEMU image and test against IDF v4.4-dev (plus minor fixes)

See merge request espressif/esp-mqtt!104

mqtt_client.c

@@ -1491,6 +1491,7 @@ static void esp_mqtt_task(void *pv)
 
     }
     esp_transport_close(client->transport);
+    outbox_delete_all_items(client->outbox);
     xEventGroupSetBits(client->status_bits, STOPPED_BIT);
 
     vTaskDelete(NULL);