Detect invalid certificate files
Detect invalid certificate files

Closes #1977

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

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