User tag changes for <=3.3.4

I found that RabbitMQ 3.3.4 separates tags with only a space, where 3.3.5 separates them with a comma and then a space. This works around that by first splitting tags by spaces, then stripping any word-final commas if they are present, so that it will work regardless of which way rabbitmqctl formats the tag list.

This has already been tested throughout my company's various environments, and all tests pass after this change.