Add support for setting up nova-spicehtml5proxy

Add a new service 'n-spice' which is off by default, but can
be enabled to turn on SPICE support in the Nova libvirt driver.
Also if neither n-novnc or n-xvnc are enabled, then disable
VNC support. This allows running in a SPICE only environment.

The spice-html5 repo will be checked out to support the Horizon
client integration

Change-Id: If74fad33a7b491450afd823758d35b06ebe72cb9
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Merge "Add support for setting up nova-spicehtml5proxy"