Puppet 3.4 compatibility fix
ignore extra tags on the user
sort the tags before setting

this isn't necessary for actual functionality but is easier for unit
tests
exchanges recreated if vhost is not default /

This should fix issue 173:
https://github.com/puppetlabs/puppetlabs-rabbitmq/issues/173

self.instances would only return the list of exchanges for the default
vhost /, this would cause a problem as any other exchange would be
recreated in every Puppet run.
Also, rabbitmqctl was used instead of rabbitmqadmin because the latest
requires the username and password of the admin user to list the
exchanges, while the first does not.
Merge pull request #175 from xcu/issue_173_recreated_exchanges

exchanges recreated if vhost is not default /
Merge pull request #160 from bobtfish/master

Puppet 3.4 compatibility fix
Merge pull request #162 from 3dna/user_tags

ignore extra tags on the user