I was looking at failed health jobs last week and found something started happening on snowballs (5 of the 7 failures):

http://validation.linaro.org/lava-server/scheduler/reports/failures?start=-7&end=0&health_check=1

lets keep an eye on this. If this continues to occur, we should probably create a new tag just for this failure and check if there's a better image to try for health checks.