debugger: don't spawn child process in remote mode

When debug in remote mode with host:port or pid, the interface
spawn child process also. If the debugger agent is running, will
get following output:

```
< Error: listen EADDRINUSE :::5858
<     at Object.exports._errnoException (util.js:734:11)
<     at exports._exceptionWithHostPort (util.js:757:20)
<     at Agent.Server._listen2 (net.js:1155:14)
<     at listen (net.js:1181:10)
<     at Agent.Server.listen (net.js:1268:5)
<     at Object.start (_debug_agent.js:21:9)
<     at startup (node.js:68:9)
<     at node.js:799:3
```

This fix won't spawn child process and no more error message was
shown.

Reviewed-By: Julien Gilli <julien.gilli@joyent.com>
PR-URL: #14172

lib/_debugger.js

@@ -1627,6 +1627,7 @@ Interface.prototype.trySpawn = function(cb) {
   this.killChild();
   assert(!this.child);
 
+  var isRemote = false;
   if (this.args.length === 2) {
     var match = this.args[1].match(/^([^:]+):(\d+)$/);
 
@@ -1635,21 +1636,13 @@ Interface.prototype.trySpawn = function(cb) {
       // `node debug localhost:5858`
       host = match[1];
       port = parseInt(match[2], 10);
-      this.child = {
-        kill: function() {
-          // TODO Do we really need to handle it?
-        }
-      };
+      isRemote = true;
     }
   } else if (this.args.length === 3) {
     // `node debug -p pid`
     if (this.args[1] === '-p' && /^\d+$/.test(this.args[2])) {
-      this.child = {
-        kill: function() {
-          // TODO Do we really need to handle it?
-        }
-      };
       process._debugProcess(parseInt(this.args[2], 10));
+      isRemote = true;
     } else {
       var match = this.args[1].match(/^--port=(\d+)$/);
       if (match) {
@@ -1661,10 +1654,13 @@ Interface.prototype.trySpawn = function(cb) {
     }
   }
 
-  this.child = spawn(process.execPath, childArgs);
+  if (!isRemote) {
+    // pipe stream into debugger
+    this.child = spawn(process.execPath, childArgs);
 
-  this.child.stdout.on('data', this.childPrint.bind(this));
-  this.child.stderr.on('data', this.childPrint.bind(this));
+    this.child.stdout.on('data', this.childPrint.bind(this));
+    this.child.stderr.on('data', this.childPrint.bind(this));
+  }
 
   this.pause();
 
@@ -1708,9 +1704,10 @@ Interface.prototype.trySpawn = function(cb) {
 
   client.on('error', connectError);
   function connectError() {
-    // If it's failed to connect 4 times then don't catch the next error
+    // If it's failed to connect 10 times then print failed message
     if (connectionAttempts >= 10) {
-      client.removeListener('error', connectError);
+      self.stdout.write(' failed, please retry\n');
+      return;
     }
     setTimeout(attemptConnect, 500);
   }
@@ -1721,10 +1718,12 @@ Interface.prototype.trySpawn = function(cb) {
     client.connect(port, host);
   }
 
-  this.child.stderr.once('data', function() {
-    setImmediate(function() {
-      self.print('connecting to port ' + port + '..', true);
-      attemptConnect();
+  self.print('connecting to ' + host + ':' + port + ' ..', true);
+  if (isRemote) {
+    attemptConnect();
+  } else {
+    this.child.stderr.once('data', function() {
+      setImmediate(attemptConnect);
     });
-  });
+  }
 };