Restore middleware connector parameters

As pointed out by Matthew Barr in review, Some of the middleware-related
parameters removed previously were in fact used to parameterize the
mcollective connector(s) to that middleware, and so should not have been
removed. This commit restores the one such found parameter (so far),
$rabbitmq_vhost.
Merge remote-tracking branch 'reidmv/pe_compatibility' into pe_compatibility