lxc-to-lxd: switch to using whitelist
lxc-to-lxd: switch to using whitelist

We keep a whitelist for supported configuration keys. We then perform a check
whether the container sets any unsupported configuration keys. We report the
first unsupported configuration key we found back to the user and the error out.

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

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