The libvirt-python library has C bindings which are very particular
about the version of its companion package (libvirt). To ensure
things run smoothly for stable releases, we opt to use the distro
packages for these and symlink the appropriate library files and
binding into the venv.
This approach has been used successfully for the ceph python bindings.
Change-Id: Id962efe16c425424715409f071c4a304f8416001