MXS-1300: Reorganize and refactor tests

The tests are now sorted by command type. This allows for more consistent
test creation as tests can be done per source code file instead of per
object type.

Added helper functions for common testing operations. The two main ones
are doCommand, which executes a MaxCtrl command and returns a result, and
verifyCommand, that executes a command and verifies the result via the
REST API.

maxctrl/test/diagnostics.js

@@ -1,9 +1,12 @@
 require('../test_utils.js')()
 
 var ctrl = require('../lib/core.js')
+var opts = { extra_args: [ '--quiet'] }
+
 var tests = [
     'list servers',
     'list services',
+    'list listeners RW-Split-Router',
     'list monitors',
     'list sessions',
     'list filters',
@@ -24,9 +27,7 @@ describe("Diagnostic commands", function() {
 
     tests.forEach(function(i) {
         it(i, function() {
-            return ctrl.execute(i.split(' '), {
-                extra_args: [ '--quiet']
-            })
+            return doCommand(i)
                 .should.be.fulfilled
         });
     })