Compute TarSum on storage of image layer content

Now, newly created/imported layers will have the checksum of
the layer diff computed and stored in the image json file.

For now, it is not an error if the computed checksum does not
match an existing checksum, only a warning message is logged. The
eventual goal is to use the checksums in the image JSON to verify
the integrity of the layer contents when doing `docker load` or
`docker pull`, and error out if it does not match.

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

Signed-off-by: Vincent Batts <vbatts@redhat.com>
LINKED CONTAINER ID PASSED TO LXC

This passed the --net=container:CONTINER_ID to lxc-start as --share-net
Docker-DCO-1.1-Signed-off-by: Abin Shahab <ashahab@altiscale.com> (github: ashahab-altiscale)
btrfs: build tag to enable showing version info

be default it is on, with build tags to disable the version info

Signed-off-by: Vincent Batts <vbatts@redhat.com>
Dockerfile: buildtags for old btrfs

Since the build uses ubuntu 14.04, which has an old btrfs, include the
buildtags needed for this old version to not break the build.

Signed-off-by: Vincent Batts <vbatts@redhat.com>
Fix typo "infortmation" in docs for `docker run`
Merge pull request #8964 from jlhawn/image_checksum

Compute TarSum on storage of image layer content
Merge pull request #9107 from ashahab-altiscale/9062-linked-container

Share network namespace of containers with lxc
Do not display empty lines in docker info if the key doesn't exists

Signed-off-by: Victor Vieux <vieux@docker.com>
Merge pull request #9131 from vieux/empty_lines_dockerinfo

Do not display empty lines in docker info if the key doesn't exists
Merge pull request #9011 from vbatts/vbatts-btrfs_information

btrfs: information for the information gods
Merge pull request #9156 from pixelistik/patch-1

Fix typo "infortmation" in docs for `docker run`