Due to a missing else the tool would previously terminate with an error
message showing that the kernel or init image didn't exist, even if it
was pulled successfully. Invoking the tool again would continue to the
next image.
Signed-off-by: Magnus Skjegstad <magnus@skjegstad.com>
`docker create` will not pull an image so we need an additional fallback.
Rework the pull and trust code so it is in one place to facilitate this.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
