MXS-1300: Add basic maxctrl tests

Added basic tests for maxctrl. They simply test that the diagnostic
commands work.

maxctrl/test/diagnostics.js

@@ -0,0 +1,35 @@
+require('../test_utils.js')()
+
+describe("Diagnostic commands", function() {
+    before(startMaxScale)
+
+    var ctrl = require('../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',
+    ]
+
+    tests.forEach(function(i) {
+        it(i, function() {
+            return ctrl.execute(i.split(' '), {
+                extra_args: [ '--quiet']
+            })
+                .should.be.fulfilled
+        });
+    })
+
+    after(stopMaxScale)
+});