Update 4 files

Modified parameter for disk size in order to fit right flavors for ML_INFN

• /kubernetes/k8s_cluster.yaml
• /kubernetes/private-net/k8s_cluster.yaml
• /kubernetes/private-net/spark_cluster.yaml
• /kubernetes/spark_cluster.yaml

All changes are successfully tested on paas-dev

assigned to @antonacci

merged

mentioned in commit 311e2a3d