Invocation of plugin-specific management tool REST API through Savanna

In some cases, users that have no direct access to the underlying infrastructure want to perform administrative tasks on Hadoop cluster via REST interface given by management tool. To provide this capability, Savanna should have the functionality to pass requests from user to the management tool. To support this functionality we should add REST API method:
/${cluster_id}/invoke_management_node/${path}

After this method called Savanna will get URL and credentials of the management tool from the plugin. Savanna will send this request to the provider specific management console and pass response to the user.