MXS-1300: Improve MaxCtrl HTTP error messages

The messages now show where the request failed and what was
requested. This should help resolve both develper and end-user problems.

Also fixed the missing logging of the output string in the `parse`
callback of the main function and cleaned up the POSTed server body.

maxctrl/lib/core.js

@@ -100,7 +100,9 @@ module.exports.execute = function(argv, opts) {
         program
             .parse(argv, {resolve: resolve, reject: reject}, function(err, argv, output) {
                 if (err) {
-                    reject(err)
+                    reject(err.message)
+                } else if (output) {
+                    logger.log(output)
                 }
             })
     })