convert precondition from array to a string

I ran into issues with this line. It could be b/c I am
using an older version of librarian-puppet. I updated the code
to make the issue go away.
Adds service to enable message bus for redhat

This is a requirement for getting libvirtd working.
Change rabbit_host/rabbit_port to rabbit_hosts array

This enable the 'rabbit_ha_queues' when many rabbit_hosts is present