lxd/daemon_images: improve log for image downloads
lxd/daemon_images: improve log for image downloads

Signed-off-by: Christian Brauner <48455ab3070520a2d174545c7239d6d0fabd9a83@canonical.com>

atxwebs/lxd,Skarlso/lxd,hallyn/lxd,techtonik/lxd,atxwebs/lxd,lxc/lxd,stgraber/lxd,mjeanson/lxd,pcdummy/lxd,hallyn/lxd,chrisglass/lxd,stgraber/lxd,Skarlso/lxd,lxc/lxd,erikmack/lxd,lxc/lxd,atxwebs/lxd,jsavikko/lxd,stgraber/lxd,jsavikko/lxd,mjeanson/lxd,lxc/lxd,Skarlso/lxd,pcdummy/lxd,lxc/lxd,akshaykarle/lxd,ollie314/lxd,akshaykarle/lxd,chrisglass/lxd,jsavikko/lxd,lxc/lxd,pcdummy/lxd,atxwebs/lxd,stgraber/lxd,techtonik/lxd,georghopp/lxd,chrisglass/lxd,hallyn/lxd,georghopp/lxd,erikmack/lxd,lxc/lxd,stgraber/lxd,hallyn/lxd,stgraber/lxd,mjeanson/lxd,akshaykarle/lxd,hallyn/lxd,erikmack/lxd,ollie314/lxd,Skarlso/lxd,hallyn/lxd,ollie314/lxd,georghopp/lxd,stgraber/lxd,techtonik/lxd