Update KpackClient#delete_image to be Idempotent

[#171900207]

Co-authored-by: Aakash Shah <ashah@pivotal.io>
Co-authored-by: Seth Boyles <sboyles@pivotal.io>

Author: Aakash Shah

lib/kubernetes/kpack_client.rb

@@ -28,6 +28,8 @@ def update_image(*args)
 
     def delete_image(name, namespace)
       @client.delete_image(name, namespace)
+    rescue Kubeclient::ResourceNotFoundError
+      nil
     rescue Kubeclient::HttpError => e
       raise CloudController::Errors::ApiError.new_from_details('KpackImageError', 'delete', e.message)
     end

spec/unit/lib/kubernetes/kpack_client_spec.rb

@@ -102,6 +102,15 @@
           subject.delete_image('resource-name', 'namespace')
         }.to raise_error(CloudController::Errors::ApiError)
       end
+
+      context 'when the image is not present' do
+        it 'returns nil' do
+          allow(kube_client).to receive(:delete_image).with('name', 'namespace').and_raise(Kubeclient::ResourceNotFoundError.new(404, 'images not found', '{"kind": "Status"}'))
+
+          image = subject.delete_image('name', 'namespace')
+          expect(image).to be_nil
+        end
+      end
     end
   end
 end