Adding a default docker registry mirror (#689)

* Adding a default docker registry mirror

This change allows the controller to start with a specified default
docker registry mirror and avoid having to specify it in all the runner*
objects.

The change is backward compatible, if a runner has a docker registry
mirror specified, it will supersede the default one.

controllers/runnerset_controller.go

@@ -51,9 +51,11 @@ type RunnerSetReconciler struct {
 	Recorder record.EventRecorder
 	Scheme   *runtime.Scheme
 
-	CommonRunnerLabels       []string
-	GitHubBaseURL            string
-	RunnerImage, DockerImage string
+	CommonRunnerLabels   []string
+	GitHubBaseURL        string
+	RunnerImage          string
+	DockerImage          string
+	DockerRegistryMirror string
 }
 
 // +kubebuilder:rbac:groups=actions.summerwind.dev,resources=runnersets,verbs=get;list;watch;create;update;patch;delete
@@ -257,7 +259,7 @@ func (r *RunnerSetReconciler) newStatefulSet(runnerSet *v1alpha1.RunnerSet) (*ap
 		Spec:       runnerSetWithOverrides.StatefulSetSpec.Template.Spec,
 	}
 
-	pod, err := newRunnerPod(template, runnerSet.Spec.RunnerConfig, r.RunnerImage, r.DockerImage, r.GitHubBaseURL, false)
+	pod, err := newRunnerPod(template, runnerSet.Spec.RunnerConfig, r.RunnerImage, r.DockerImage, r.DockerRegistryMirror, r.GitHubBaseURL, false)
 	if err != nil {
 		return nil, err
 	}