Add loop_start to ensure all messages are published

[mjrsnyder]

I was having an issue where I could see all the messages being published in the debug logs but not all the messages made it to the broker. When using the --all flag the first few messages would make it but I would only get down to temperature messages occasionally. The MQTT broker would log Socket error on client <client id>, disconnecting. presumably before the client finished publishing all messages. This was happening over a somewhat compromised WiFi connection on older hardware.

Adding loop_start() resolved the issue for me. I'm now getting all data and I no longer get errors in the broker log.