proxy: should add PingPeriod for websocket translator

IIUC, before using the translator handler, the ping data can be delivered from
the client to the runtime side since kube-apiserver does not parse any client
data. However, with WebSocket, the server responds with a pong to the client
without forwarding the data to the runtime side. If a proxy is present, it may
close the connection due to inactivity. SPDY's PingPeriod can help address this
issue.

Signed-off-by: Wei Fu <fuweid89@gmail.com>
Co-authored-by: Antonio Ojea <aojea@google.com>
(cherry picked from commit dc59c0246fb407dcf035afc224f63fcf0da8244e)
Signed-off-by: Wei Fu <fuweid89@gmail.com>

test/e2e/kubectl/kubectl.go

@@ -500,6 +500,16 @@ var _ = SIGDescribe("Kubectl client", func() {
 			}
 		})
 
+		// https://issues.k8s.io/128314
+		f.It(f.WithSlow(), "should support exec idle connections", func(ctx context.Context) {
+			ginkgo.By("executing a command in the container")
+
+			execOutput := e2ekubectl.RunKubectlOrDie(ns, "exec", podRunningTimeoutArg, simplePodName, "--", "/bin/sh", "-c", "sleep 320 && echo running in container")
+			if expected, got := "running in container", strings.TrimSpace(execOutput); expected != got {
+				framework.Failf("Unexpected kubectl exec output. Wanted %q, got %q", expected, got)
+			}
+		})
+
 		ginkgo.It("should support exec through kubectl proxy", func(ctx context.Context) {
 			_ = getTestContextHost()