bqx: config changes to queries do not reload automatically

[stephen-soltesz]

This has been a long standing issue. If bqx queries change, they are updated in the configmap, but the bqx never refreshes them without manually bouncing the pod.

v1.0 of the bqx tried to resolve this but it does not wai with k8s configmap file mounts m-lab/prometheus-bigquery-exporter#25

The work around for now is to manually delete the pod, or to twiddle the k8s bqx config during a deploy, e.g. a neutral label change.