Compute TarSum of image layer data when installing

Adds a new `Checksum` field to the current image format
to store the result of the tarsum of the file system changes.

Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)
Remove `jsonData` argument from `image.StoreImage`

The argument specified the json data to save to disk when registering
a new image into the image graph. If it is nil, then the given image
is serialized to json and that is written by default. This default
behavior is sufficient because the given image was originally deserialzed
from this jsonData to begin with.

Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)
Remove unused "image_set" job

A quick grep of the code base shows that the "image_set" job
registered by the TagStore is not used.

Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)
AUFS Diff/ApplyDiff excludes /.wh..wh.* files

Also includes Checksum field in `docker inspect` output for images.
Correcly close layerData decompress/reader wrapper when storing images.
Remove imgJSON from call to graph.Register when pulling an image.

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)