Fix a few e2e references to allow gke to test dogfood builds

cluster/gke/util.sh

@@ -99,7 +99,7 @@ function verify-prereqs() {
     sudo_prefix="sudo"
   fi
   ${sudo_prefix} gcloud ${gcloud_prompt:-} components update preview || true
-  ${sudo_prefix} gcloud ${gcloud_prompt:-} components update alpha|| true
+  ${sudo_prefix} gcloud ${gcloud_prompt:-} components update "${CMD_GROUP}"|| true
   ${sudo_prefix} gcloud ${gcloud_prompt:-} components update kubectl|| true
   ${sudo_prefix} gcloud ${gcloud_prompt:-} components update || true
 }

hack/jenkins/e2e.sh

@@ -127,7 +127,7 @@ if [[ "${E2E_UP,,}" == "true" ]]; then
             #       code=400,message=cluster.cluster_api_versionmustbeoneof:
             #       0.15.0,0.16.0.
             # The command should error, so we throw an || true on there.
-            msg=$(gcloud alpha container clusters create this-wont-work \
+            msg=$(gcloud ${CMD_GROUP:-alpha} container clusters create this-wont-work \
                 --zone=us-central1-f --cluster-api-version=0.0.0 2>&1 \
                 | tr -d '[[:space:]]') || true
             # Strip out everything before the final colon, which gives us just