data_handler.py: add pause between flushing queue
data_handler.py: add pause between flushing queue

cllamb0/dosenet-raspberrypi,yarocoder/dosenet-raspberrypi,tybtab/dosenet-raspberrypi,tybtab/dosenet-raspberrypi,bearing/dosenet-raspberrypi,cllamb0/dosenet-raspberrypi,bearing/dosenet-raspberrypi,yarocoder/dosenet-raspberrypi