lxd/qemu: Add support for spice agent
lxd/qemu: Add support for spice agent

This adds two additional named serial ports for interacting with guest
services over SPICE.

With those in place, clipboard sharing, improved cursor/resolution
management and folder sharing are all possible.

Signed-off-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>

hallyn/lxd,hallyn/lxd,lxc/lxd,mjeanson/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,mjeanson/lxd,mjeanson/lxd,Skarlso/lxd,lxc/lxd,atxwebs/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,Skarlso/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,Skarlso/lxd,hallyn/lxd,atxwebs/lxd,hallyn/lxd,hallyn/lxd,stgraber/lxd,atxwebs/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd,Skarlso/lxd