Use a tempfile for image uploads
Use a tempfile for image uploads

Closes #1508

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

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