Make ping test fail on connection error.
Make ping test fail on connection error.

Signed-off-by: Orne Brocaar <59bd0a3ff43b32849b319e645d4798d8a5d1e889@brocaar.com>

choonkeat/paho.mqtt.golang,choonkeat/paho.mqtt.golang,choonkeat/paho.mqtt.golang