Nova: Only start messagebus on RedHat.

This work around is only required on RedHat so use operatingsystem
instead of osfamily.
Only set special_service_provider on RHEL.

Updates the params.pp so that special_service_provider is set
to 'init' on RHEL only. This gets used to startup libvirtd.

This fixes issues using the Nova compute/libvirt module on
Fedora.
Set defaults for flat_interface and fixed_range.

Updates the Nova flatdhcp module so that it contains
default settings for flat_interface and fixed_range. These
setting match what Nova uses.
Add support for configuring qpid.