Google Kubernetes Engine plugin currently can only verify deployment with `recreate` strategy, and first deployment of pods with `rolling update` strategy. However this doesn't work during deployment update. It sees that the minimum number of replicas is correct (which can happen multiple times during a rollout before all replicas have been updated) and it will mark the deployment as complete.

This PR enables to correctly verify deployments with rolling update strategy https://github.com/jenkinsci/google-kubernetes-engine-plugin/pull/321