Wait for apiserver to become healthy before starting agent controllers

It is possible that the apiserver may serve read requests but not allow
writes yet, in which case flannel will crash on startup when trying to
configure the subnet manager.

Fix this by waiting for the apiserver to become fully ready before
starting flannel and the network policy controller.

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>

pkg/agent/run.go

@@ -35,6 +35,7 @@ import (
 	"k8s.io/client-go/kubernetes"
 	v1 "k8s.io/client-go/kubernetes/typed/core/v1"
 	"k8s.io/client-go/tools/clientcmd"
+	"k8s.io/controller-manager/app"
 )
 
 var (
@@ -98,6 +99,9 @@ func run(ctx context.Context, cfg cmds.Agent, proxy proxy.Proxy) error {
 	if err != nil {
 		return err
 	}
+
+	app.WaitForAPIServer(coreClient, 30*time.Second)
+
 	if !nodeConfig.NoFlannel {
 		if err := flannel.Run(ctx, nodeConfig, coreClient.CoreV1().Nodes()); err != nil {
 			return err