Set RBAC support behind a feature flag.

This is the same as with adding an existing cluster

app/services/clusters/gcp/finalize_creation_service.rb

@@ -48,9 +48,8 @@ module Clusters
         Clusters::Gcp::Kubernetes::FetchKubernetesTokenService.new(kube_client).execute
       end
 
-      # GKE Clusters have RBAC enabled on Kubernetes >= 1.6
       def authorization_type
-        'rbac'
+        Feature.enabled?(:rbac_clusters) ? 'rbac' : 'abac'
       end
 
       def kube_client

spec/services/clusters/gcp/finalize_creation_service_spec.rb

@@ -59,6 +59,30 @@ describe Clusters::Gcp::FinalizeCreationService do
               metadata_name: 'gitlab-token-Y1a',
               token: Base64.encode64(token)
             } )
+
+          stub_feature_flags(rbac_clusters: false)
+        end
+
+        it_behaves_like 'success'
+
+        it 'has corresponded data' do
+          described_class.new.execute(provider)
+          cluster.reload
+          provider.reload
+          platform.reload
+
+          expect(provider.endpoint).to eq(endpoint)
+          expect(platform.api_url).to eq(api_url)
+          expect(platform.ca_cert).to eq(Base64.decode64(load_sample_cert))
+          expect(platform.username).to eq(username)
+          expect(platform.password).to eq(password)
+          expect(platform.authorization_type).to eq('abac')
+          expect(platform.token).to eq(token)
+        end
+
+        context 'rbac_clusters feature enabled' do
+          before do
+            stub_feature_flags(rbac_clusters: true)
           end
 
           it_behaves_like 'success'
@@ -78,6 +102,7 @@ describe Clusters::Gcp::FinalizeCreationService do
             expect(platform.token).to eq(token)
           end
         end
+      end
 
       context 'when default-token is not found' do
         before do