libvirt plugin "parallels" support

We're in the process of establishing the CI testing with
Parallels Cloud Server plugin for libvirt.
Currently we use local clone of devstack in our infrastructure,
but we want to switch to upstream

requires extra customization of nova.conf and glance-api.conf:
nova.conf should have "images_type" and "connection_uri"
defined, and glance-api.conf to have "ploop" in disk formats

Implements: blueprint pcs-support
Change-Id: I0b073359fda8b4531cae7b8946eb52a561c82857
Merge "libvirt plugin "parallels" support"