cmd/tailscale: add "tailscale debug hostinfo" subcommand

Change-Id: Ifa09364d42e0516fdf80feddaf33c95880228049
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscale/cli/debug.go

@@ -22,6 +22,7 @@ import (
 
 	"github.com/peterbourgon/ff/v3/ffcli"
 	"tailscale.com/client/tailscale"
+	"tailscale.com/hostinfo"
 	"tailscale.com/ipn"
 	"tailscale.com/paths"
 	"tailscale.com/safesocket"
@@ -65,6 +66,11 @@ var debugCmd = &ffcli.Command{
 			Exec:      runEnv,
 			ShortHelp: "print cmd/tailscale environment",
 		},
+		{
+			Name:      "hostinfo",
+			Exec:      runHostinfo,
+			ShortHelp: "print hostinfo",
+		},
 		{
 			Name:      "local-creds",
 			Exec:      runLocalCreds,
@@ -270,6 +276,13 @@ func runEnv(ctx context.Context, args []string) error {
 	return nil
 }
 
+func runHostinfo(ctx context.Context, args []string) error {
+	hi := hostinfo.New()
+	j, _ := json.MarshalIndent(hi, "", "  ")
+	os.Stdout.Write(j)
+	return nil
+}
+
 func runDaemonGoroutines(ctx context.Context, args []string) error {
 	goroutines, err := tailscale.Goroutines(ctx)
 	if err != nil {