Missing Zone label

[rghetia]

Kube operator injects following resources labels with resource Type as k8s.

Label	Description	Example
k8s.cluster.name	The name of the cluster that the pod is running in.	opencensus-cluster
k8s.namespace.name	The name of the namespace that the pod is running in.	default
k8s.pod.name	The name of the pod.	opencensus-pod-autoconf
k8s.deployment.name	The name of the deployment.	opencensus

This gets translated to 'k8s_container` resource in Stackdriver exporter as per this mapping

The problem here is that there is no Zone label injected by kube operator. As a result there is no location label after conversion in SD Exporter. 'location' being a mandatory label for 'k8s_container' resource type, the timeseries gets rejected due to missing location label.

This could be designated as SD Exporter issue but kube operator becomes useless for SD Exporter without location. Anyone who wants to use these resource labels would have to add gke.Detect() in SD exporter option . Hence the issue is opened here to add Zone label support.