boot: extract file extension to support dots in image path
boot: extract file extension to support dots in image path

AnnikaH/IncludeOS,alfred-bratterud/IncludeOS,AndreasAakesson/IncludeOS,ingve/IncludeOS,mnordsletten/IncludeOS,AnnikaH/IncludeOS,alfred-bratterud/IncludeOS,ingve/IncludeOS,mnordsletten/IncludeOS,hioa-cs/IncludeOS,AndreasAakesson/IncludeOS,mnordsletten/IncludeOS,hioa-cs/IncludeOS,alfred-bratterud/IncludeOS,ingve/IncludeOS,AndreasAakesson/IncludeOS,ingve/IncludeOS,ingve/IncludeOS,AnnikaH/IncludeOS,AndreasAakesson/IncludeOS,mnordsletten/IncludeOS,hioa-cs/IncludeOS,hioa-cs/IncludeOS,AndreasAakesson/IncludeOS,alfred-bratterud/IncludeOS,mnordsletten/IncludeOS,alfred-bratterud/IncludeOS,mnordsletten/IncludeOS,AnnikaH/IncludeOS,hioa-cs/IncludeOS,AnnikaH/IncludeOS,AndreasAakesson/IncludeOS