improve Windows Docker clean slate

hack/jenkins/windows_integration_test_docker.ps1

@@ -48,12 +48,11 @@ echo "Docker_Windows" | gsutil cp - "$append_tmp"
 gsutil compose "$started_environments" "$append_tmp" "$started_environments"
 gsutil rm "$append_tmp"
 
-# Remove unused images and containers
-docker system prune --all --force
-
-
 ./out/minikube-windows-amd64.exe delete --all
 
+# Remove unused images and containers
+docker system prune --all --force --volumes
+
 ./out/windows_integration_setup.ps1
 
 docker ps -aq | ForEach -Process {docker rm -fv $_}