lxd/instance/drivers/driver/qemu: Ensure bootindex is generated in a stable manner in deviceBootPriorities
lxd/instance/drivers/driver/qemu: Ensure bootindex is generated in a stable manner in deviceBootPriorities

Devices that don't have an explicit boot.priority were being given a random boot index.

This fixes it by re-using the device's Sorted() function which orders them the say order they are setup for predictability.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

stgraber/lxd,atxwebs/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,atxwebs/lxd,lxc/lxd,hallyn/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,atxwebs/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd