Rename DOCKER_CONFIG envvar to DOCKER_CERT_PATH

DOCKER_CONFIG was introduced in #6984.

We may use "config" for other purposes (e.g. #7232). Until we
have made a design decision around how configuration files will
work, DOCKER_CERT_PATH is a much safer name to rely on for future
compatibility.

Docker-DCO-1.1-Signed-off-by: Ben Firshman <ben@firshman.co.uk> (github: bfirsh)
Merge pull request #7349 from knan-linpro/master

networking.md: Networking between containers works without ip_forward
Add contrib/nuke-graph-directory.sh script to clean out old /var/lib/docker directories much more easily

Signed-off-by: Andrew Page <admwiggin@gmail.com>
Merge pull request #6909 from LK4D4/prune_cmd_on_entrypoint_setting_#5147

Cleanup cmd on entrypoint setting
Docker should use /var/lib/container/tmp for large temporary files.

/tmp is often a tmpfs file system and large temporary files could cause
docker commands to fail.  Also using /tmp potentially allows users on the
system to get access to content, or even attack the content.  Moving the tmpdir to
/var/lib/container/tmp will protect the data.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)

Conflicts:
	docker/docker.go
Merge pull request #7412 from bfirsh/rename-docker-config

Rename DOCKER_CONFIG envvar to DOCKER_CERT_PATH
Merge pull request #7186 from jamtur01/community

Added proposed Docker Community Guidelines
style, grammar, spelling fixes.

Signed-off-by: Marc Tamsky <mtamsky@gmail.com> (github: tamsky)
Update libcontainer to 5589d4d879f1d7e31967a927d3e

Signed-off-by: Michael Crosby <michael@docker.com>
Made requested changes (capitalization)
add warning re: changing value of `dm.basesize`.

Signed-off-by: Marc Tamsky <mtamsky@gmail.com> (github: tamsky)
Move "image_export" to graph/export.go

Signed-off-by: Solomon Hykes <solomon@docker.com>
Move "image_history" to graph/history.go

Signed-off-by: Solomon Hykes <solomon@docker.com>
Move "images" to graph/list.go

Signed-off-by: Solomon Hykes <solomon@docker.com>
Move "viz" to graph/viz.go

Signed-off-by: Solomon Hykes <solomon@docker.com>
Move "load" to graph/load.go

Signed-off-by: Solomon Hykes <solomon@docker.com>
Move "import" to graph/import.go

Signed-off-by: Solomon Hykes <solomon@docker.com>
Move "image_delete" to daemon/image_delete.go

Note: this cannot yet be moved to graph/ because of a lingering
dependency on daemon. This has been noted in a FIXME.

Signed-off-by: Solomon Hykes <solomon@docker.com>
Move "image_tag" and "tag" to graph/tag.go

Note: these 2 jobs should be merged into one. This was noted in a FIXME.

Signed-off-by: Solomon Hykes <solomon@docker.com>
Move some integration tests to integration-cli

Signed-off-by: Tibor Vass <teabee89@gmail.com>