Set rabbitmq package_provider to yum

Set rabbitmq package_provider to yum

When deploying with EnablePackageInstall:True, the rabbitmq puppet
module defaults to the rpm package provider, which then tries to "rpm -i
undef" since we are setting rabbitmq::package_source to undef. Instead
of using the rpm provider at all, we should just use the yum provider to
install whatever rabbitmq rpm's are found in enabled repos.

Change-Id: I29365e675bfde676fde7a54dfc6c660c3970f50a
Partially-implements: blueprint split-stack-software-configuration