MXS-1300: Disable all output with --quiet

As the option is currently only used for testing, it's better to have it
produce no output at all.

maxctrl/common.js

@@ -26,7 +26,8 @@ module.exports = function() {
     this.maxctrl = function(argv) {
 
         if (argv.quiet) {
-            this.logger = new consoleLib.Console(fs.createWriteStream('/dev/null'), process.stderr)
+            this.logger = new consoleLib.Console(fs.createWriteStream('/dev/null'),
+                                                 fs.createWriteStream('/dev/null'))
         }
 
         this.argv = argv

maxctrl/core.js

@@ -55,7 +55,7 @@ program
     })
     .option('q', {
         alias: 'quiet',
-        describe: 'Output only errors',
+        describe: 'Silence all output',
         default: 'false',
         type: 'boolean'
     })