MXS-1300: Use native promises for requests

The request-promise-native package adds support for request with native
promises. This is a convenient way to synchronize multiple HTTP requests.

The functions are changed to use promises to make testing easier. With
promises, the testing code can use the chai-as-promised library.

There are a few cases where doRequest is called with a callback that again
calls doAsyncRequest. With multiple hosts, this causes each command to be
propagated to all servers. This is a design flaw of the current multi-host
mode and needs to be changed.

Changed maxctrl.js to wait on the promises to silence some warnings if the
promise rejections are ignored.

maxctrl/maxctrl.js

@@ -13,18 +13,14 @@
 
 'use strict';
 
-var argv = process.argv
+var maxctrl = require('./core.js')
 
 // Mangle the arguments if we are being called from the command line
-if (argv[0] == process.execPath) {
-    argv.shift()
+if (process.argv[0] == process.execPath) {
+    process.argv.shift()
     // The first argument is always the script
-    argv.shift()
+    process.argv.shift()
 }
 
-require('./core.js')(argv)
-    .then(function(output){
-        if (output.length > 0) {
-            console.log(output)
-        }
-    }, console.log)
+maxctrl(process.argv)
+    .then(function(out) {}, function(out) {})