MXS-1354: Add creation of basic/admin users to maxctrl

The type of the created user can now be specified with the --type option.

Expanded tests that cover the user creation. Also added a test case that
checks that basic users are only allowed to read through the REST API.

server/core/test/rest-api/test/users.js

@@ -9,6 +9,7 @@ describe("Users", function() {
             id: "user1",
             type: "inet",
             attributes: {
+                account: "admin"
             }
         }
     }