This commit adds a command line flag, "--check-all". If true, the
behavior requested by #112 is used (i.e., stopped containers are updated
but not restarted). If false, the previous behavior is used (ignore
stopped containers entirely).
Since Zodiac always uses image IDs for deployments we can relay on the
standard container image field to determine the image that was used to
start the container. Luckily, Zodiac writes the original image name to a
label in the container metadata. If we find that Zodiac-specific label
on a running container we will use the associated value when trying to
determine if the container's image has changed.
