MXS-1929: Improve JSON type error messages

If an invalid value or type is given to the REST API, having the expected
type as well as the given type make problem resolution easier.

Also added a value check into MaxCtrl for listener ports.

maxctrl/lib/create.js

@@ -222,6 +222,10 @@ exports.builder = function(yargs) {
                 .usage('Usage: create listener <service> <name> <port>')
         }, function(argv) {
 
+            if (!Number.isInteger(argv.port)) {
+                throw "'" + argv.port + "' is not a valid value for port"
+            }
+
             var listener = {
                 'data': {
                     'id': argv.name,