Add GKE 1.6 CIS benchmark for GCP environment (#1672)

* Add config entries for GKE 1.6 controls

* Add gke1.6 control plane recommendations

* Add gke-1.6.0 worker node recommendations

* Add gke-1.6.0 policy recommendations

* Add managed services and policy recommendation

* Add master recommendations

* Fix formatting across gke-1.6.0 files

* Add gke-1.6.0 benchmark selection based on k8s version

* Workaround: hardcode kubelet config path for gke-1.6.0

* Fix tests for makeIPTablesUtilChaings

* Change scored field for all node tests to true

* Fix kubelet file permission to check for

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Co-authored-by: afdesk <work@afdesk.com>