MXS-1300: Un-modularize the core

Making the core a module proved to bring more problems than it solved. For
the sake of simplicity in installation and code coverage reporting, the
core is now completely contained in the `lib/` directory.

Also added preliminary coverage reporting with nyc.

maxctrl/test/diagnostics.js

@@ -1,27 +1,27 @@
 require('../test_utils.js')()
 
+var ctrl = require('../lib/core.js')
+var tests = [
+    'list servers',
+    'list services',
+    'list monitors',
+    'list sessions',
+    'list filters',
+    'list modules',
+    'list users',
+    'list commands',
+    'show server server1',
+    'show service RW-Split-Router',
+    'show monitor MySQL-Monitor',
+    'show session 5',
+    'show filter Hint',
+    'show module readwritesplit',
+    'show maxscale',
+]
+
 describe("Diagnostic commands", function() {
     before(startMaxScale)
 
-    var ctrl = require('maxctrl-core')
-    var tests = [
-        'list servers',
-        'list services',
-        'list monitors',
-        'list sessions',
-        'list filters',
-        'list modules',
-        'list users',
-        'list commands',
-        'show server server1',
-        'show service RW-Split-Router',
-        'show monitor MySQL-Monitor',
-        'show session 5',
-        'show filter Hint',
-        'show module readwritesplit',
-        'show maxscale',
-    ]
-
     tests.forEach(function(i) {
         it(i, function() {
             return ctrl.execute(i.split(' '), {