fix(gulp): let gulp handle its own errors

lib/cli.js

@@ -142,7 +142,11 @@ Cli.run = function run(processArgv) {
 
       return Q.nfcall(gulp.start.bind(gulp), argv._[0] + ':before').then(
         function(){
-          // Only some tasks return promises
+          // Only some commands return promises
+          return Q.fcall(taskInstance.run.bind(taskInstance), Cli, argv);
+        },
+        function(e){ //task error, let gulp handle it
+          // Only some commands return promises
           return Q.fcall(taskInstance.run.bind(taskInstance), Cli, argv);
         }
       ).then(function(){
@@ -199,7 +203,7 @@ function logEvents(gulpInst) {
   });
 
   gulpInst.on('task_err', function(e) {
-    var msg = formatError(e);
+    var msg = formatGulpError(e);
     var time = prettyTime(e.hrDuration);
     gutil.log(
       '\'' + chalk.cyan(e.task) + '\'',
@@ -218,6 +222,26 @@ function logEvents(gulpInst) {
   // });
 }
 
+// Format orchestrator errors
+function formatGulpError(e) {
+  if (!e.err) {
+    return e.message;
+  }
+
+  // PluginError
+  if (typeof e.err.showStack === 'boolean') {
+    return e.err.toString();
+  }
+
+  // Normal error
+  if (e.err.stack) {
+    return e.err.stack;
+  }
+
+  // Unknown (string, number, etc.)
+  return new Error(String(e.err)).stack;
+}
+
 Cli.getBooleanOptionsForTask = function getBooleanOptionsForTask(task) {
   var availableTaskOptions = task.options;
   var booleanOptions = [];