Adds Libvirt Handler

JIRA: N/A

Adds a handler which can control the libvirt hypervisor
on the remote host, in order to define the vm's and networks
that are needed for an OPNFV deployment.
Also adds the domain and network objects, which are simple abstractions
of virtual machines and networks.

Change-Id: Ia836e7b080b8bca220d5fdf6eb72b6c580cab4d1
Signed-off-by: Parker Berberian <pberberian@iol.unh.edu>