safesocket: print full lsof command on failure

This makes it easier to manually run the command
to discover why it is failing.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

safesocket/safesocket_darwin.go

@@ -53,15 +53,16 @@ func localTCPPortAndTokenDarwin() (port int, token string, err error) {
 	// The current process is running outside the sandbox, so use
 	// lsof to find the IPNExtension:
 
-	out, err := exec.Command("lsof",
+	cmd := exec.Command("lsof",
 		"-n",                             // numeric sockets; don't do DNS lookups, etc
 		"-a",                             // logical AND remaining options
 		fmt.Sprintf("-u%d", os.Getuid()), // process of same user only
 		"-c", "IPNExtension",             // starting with IPNExtension
 		"-F", // machine-readable output
-	).Output()
+	)
+	out, err := cmd.Output()
 	if err != nil {
-		return 0, "", fmt.Errorf("failed to run lsof looking for IPNExtension: %w", err)
+		return 0, "", fmt.Errorf("failed to run '%s' looking for IPNExtension: %w", cmd, err)
 	}
 	bs := bufio.NewScanner(bytes.NewReader(out))
 	subStr := []byte(".tailscale.ipn.macos/sameuserproof-")