Correct RabbitMQ plugin management command name

The RMQ module was using an incorrect command to enable/disable plugins.

	$ rabbitmq-plugins
	Error: could not recognise command
	Usage:
	rabbitmq-plugins <command> [<command options>] 

	Commands:
	    list [-v] [-m] [-E] [-e] [<pattern>]
	    enable <plugin> ...
	    disable <plugin> ...