Stop installing libvirt on baremetal nodes.

As per bug 1191649 the presence of libvirt on the baremetal undercloud
node causes routing to fail, as the node ends up with a
192.168.122.0/24 virbr0 network. Fix this by splitting out some of the
kvm specific bits of boot-stack.

Change-Id: Ie7bba9d2bceb3720fc9074e197da4c3999f1d509
Merge "Stop installing libvirt on baremetal nodes."