Parameterize the libvirt_virt_type parameter so it can be overridden
Parameterize the libvirt_virt_type parameter so it can be overridden

When running puppet-openstack-integration in certain contexts, for
example outside of the gate, we might want to choose a different
hypervisor such as KVM.
Making it a parameter will allow it to be overridden by hiera
easily.

Change-Id: Ie80740b67561ca21e1e81e9e571e66e8d505d940

openstack/puppet-openstack-integration,openstack/puppet-openstack-integration,openstack/puppet-openstack-integration