Labels can be overriden on cluster creation, and should take precendence
against the cluster template when passed. When not passed, they are filled
with the ones from the template.
Fix the setting of kube_tag on the template definition, we were taking the
cluster template and ignoring cluster.
Change-Id: I8fff6f15a780c74b1f09e7238472620e8f93b532
Closes-Bug: #1739422