Add unit test to verify Resource Label map overwrite bug.
Add unit test to verify Resource Label map overwrite bug.

kawych/k8s-stackdriver,GoogleCloudPlatform/k8s-stackdriver,kawych/k8s-stackdriver,kawych/k8s-stackdriver,GoogleCloudPlatform/k8s-stackdriver,kawych/k8s-stackdriver,GoogleCloudPlatform/k8s-stackdriver