lxd-images: Better handle download failures
lxd-images: Better handle download failures

Closes #544

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

pcdummy/lxd,Malizor/lxd,dvbportal/osx-lxd,lxc/lxd,jensg-st/lxd,atxwebs/lxd,Skarlso/lxd,Skarlso/lxd,pcdummy/lxd,akshaykarle/lxd,stgraber/lxd,achanda/lxd,basvanbeek/lxd,yura-pakhuchiy/lxd,jsavikko/lxd,lxc/lxd,yura-pakhuchiy/lxd,hallyn/lxd,beni55/lxd,lxc/lxd,Malizor/lxd,jsavikko/lxd,rrva/lxd,atxwebs/lxd,akshaykarle/lxd,techtonik/lxd,beni55/lxd,erikmack/lxd,dustinkirkland/lxd,smoser/lxd,rcj4747/lxd,mikemccracken/lxd,rrva/lxd,benaryorg/lxd,dustinkirkland/lxd,stgraber/lxd,benaryorg/lxd,lxc/lxd,benaryorg/lxd,smoser/lxd,stgraber/lxd,hallyn/lxd,dustinkirkland/lxd,dvbportal/osx-lxd,stgraber/lxd,jumpstarter-io/lxd,Skarlso/lxd,techtonik/lxd,ollie314/lxd,pcdummy/lxd,chrisglass/lxd,lxc/lxd,hallyn/lxd,atxwebs/lxd,mjeanson/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,chrisglass/lxd,hallyn/lxd,rcj4747/lxd,ericsnowcurrently/lxd,mikemccracken/lxd,georghopp/lxd,jensg-st/lxd,erikmack/lxd,mjeanson/lxd,ollie314/lxd,jsavikko/lxd,basvanbeek/lxd,mjeanson/lxd,akshaykarle/lxd,mikemccracken/lxd,chrisglass/lxd,beni55/lxd,ollie314/lxd,Malizor/lxd,sl1pm4t/lxd,georghopp/lxd,sl1pm4t/lxd,techtonik/lxd,atxwebs/lxd,jumpstarter-io/lxd,lxc/lxd,achanda/lxd,smoser/lxd,jumpstarter-io/lxd,erikmack/lxd,rcj4747/lxd,hallyn/lxd,jensg-st/lxd,sl1pm4t/lxd,georghopp/lxd,dvbportal/osx-lxd,yura-pakhuchiy/lxd,Skarlso/lxd,hallyn/lxd,ericsnowcurrently/lxd,rrva/lxd,lxc/lxd,basvanbeek/lxd,achanda/lxd,ericsnowcurrently/lxd