tstest/integration: add integration test for Tailnet Lock

This patch adds an integration test for Tailnet Lock, checking that a node can't
talk to peers in the tailnet until it becomes signed.

This patch also introduces a new package `tstest/tkatest`, which has some helpers
for constructing a mock control server that responds to TKA requests. This allows
us to reduce boilerplate in the IPN tests.

Updates tailscale/corp#33599

Signed-off-by: Alex Chan <alexc@tailscale.com>

tstest/integration/integration.go

@@ -918,7 +918,7 @@ func (n *TestNode) Ping(otherNode *TestNode) error {
 	t := n.env.t
 	ip := otherNode.AwaitIP4().String()
 	t.Logf("Running ping %v (from %v)...", ip, n.AwaitIP4())
-	return n.Tailscale("ping", ip).Run()
+	return n.Tailscale("ping", "--timeout=1s", ip).Run()
 }
 
 // AwaitListening waits for the tailscaled to be serving local clients
@@ -1077,6 +1077,46 @@ func (n *TestNode) MustStatus() *ipnstate.Status {
 	return st
 }
 
+// PublicKey returns the hex-encoded public key of this node,
+// e.g. `nodekey:123456abc`
+func (n *TestNode) PublicKey() string {
+	tb := n.env.t
+	tb.Helper()
+	cmd := n.Tailscale("status", "--json")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		tb.Fatalf("running `tailscale status`: %v, %s", err, out)
+	}
+
+	type Self struct{ PublicKey string }
+	type StatusOutput struct{ Self Self }
+
+	var st StatusOutput
+	if err := json.Unmarshal(out, &st); err != nil {
+		tb.Fatalf("decoding `tailscale status` JSON: %v\njson:\n%s", err, out)
+	}
+	return st.Self.PublicKey
+}
+
+// NLPublicKey returns the hex-encoded network lock public key of
+// this node, e.g. `tlpub:123456abc`
+func (n *TestNode) NLPublicKey() string {
+	tb := n.env.t
+	tb.Helper()
+	cmd := n.Tailscale("lock", "status", "--json")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		tb.Fatalf("running `tailscale lock status`: %v, %s", err, out)
+	}
+	st := struct {
+		PublicKey string `json:"PublicKey"`
+	}{}
+	if err := json.Unmarshal(out, &st); err != nil {
+		tb.Fatalf("decoding `tailscale lock status` JSON: %v\njson:\n%s", err, out)
+	}
+	return st.PublicKey
+}
+
 // trafficTrap is an HTTP proxy handler to note whether any
 // HTTP traffic tries to leave localhost from tailscaled. We don't
 // expect any, so any request triggers a failure.