Enable stackdriver agents for GKE by default.

* We want to enable the stackdriver monitoring agents by default. This allows
  pod logs to be fetched by pod label which is very valuable.

* To enable this we need to use the v1beta1 API for GKE
https://cloud.google.com/kubernetes-engine/docs/reference/api-organization#beta

* Remove the field CLUSTER_VERSION from kfctl.sh
  This was added in kubeflow#1888 but it doesn't look like it was actually being
  use to set the CLUSTER_VERSION; it looks like cluster-version is set
  in the deployment manager config cluster-kubeflow.yaml

Related to kubeflow#1757

scripts/kfctl.sh

@@ -12,8 +12,12 @@ set -xe
 
 ENV_FILE="env.sh"
 SKIP_INIT_PROJECT=false
-CLUSTER_VERSION="1.10"
-GKE_API_VERSION="v1"
+
+# To enable GKE beta features we need to use the v1beta1 API.
+# https://cloud.google.com/kubernetes-engine/docs/reference/api-organization#beta
+# We currently use this by default so we can enable the new stackdriver
+# logging agents.
+GKE_API_VERSION="v1beta1"
 
 DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" > /dev/null && pwd)"
 source "${DIR}/util.sh"
@@ -85,11 +89,6 @@ createEnv() {
 
       echo PROJECT_NUMBER=${PROJECT_NUMBER} >> ${ENV_FILE}
 
-      # "1.X": picks the highest valid patch+gke.N patch in the 1.X version
-      # https://cloud.google.com/kubernetes-engine/docs/reference/rest/v1/projects.zones.clusters
-      echo "Setting cluster version to ${CLUSTER_VERSION}"
-      echo CLUSTER_VERSION=${CLUSTER_VERSION} >> ${ENV_FILE}
-
       echo GKE_API_VERSION=${GKE_API_VERSION} >> ${ENV_FILE}
       ;;
     *)