Added proposed Docker Community Guidelines

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
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)
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
Update libcontainer to 5589d4d879f1d7e31967a927d3e

Signed-off-by: Michael Crosby <michael@docker.com>
Merge pull request #6456 from rhatdan/tmpdir

Docker should use /var/lib/docker/tmp for large temporary files.
Fix TestBuildForbiddenContextPath after TMPDIR change

Signed-off-by: Tibor Vass <teabee89@gmail.com>
Update hack/vendor.sh to use libcontainer's update-vendor.sh script as the source of truth for libcontainer deps and not include them in Docker's repo twice

Signed-off-by: Andrew Page <admwiggin@gmail.com>
Update vendor with the updated canonical deps from libcontainer

Signed-off-by: Andrew Page <admwiggin@gmail.com>
Fix integration tests by adding DOCKER_TMPDIR env in the test init function

Signed-off-by: Tibor Vass <teabee89@gmail.com>
Merge pull request #27 from tianon/update-libcontainer

Update hack/vendor.sh to use libcontainer's update-vendor.sh script as the source of truth for libcontainer deps and not include them in Docker's repo twice
Merge pull request #7448 from tiborvass/fix-tmpdir-integration-tests

Fix tmpdir integration tests
Merge pull request #7428 from crosbymichael/update-libcontainer-aug2

Update libcontainer to 5589d4d879f1d7e31967a927d3e
Subsystems can register cleanup handlers with Engine.OnShutdown

Signed-off-by: Solomon Hykes <solomon@docker.com>
Move signal handling code to pkg/signal.Trap

Signed-off-by: Solomon Hykes <solomon@docker.com>
Cleanup: refactor shutdown and signal handling facility

This disentangles the following functions, which were previously all mixed together:

* 1) Waiting for jobs to terminate when shutting down
* 2) Handling signals in the Docker daemon
* 3) Per-subsystem cleanup handlers
* 4) pidfile management

Responsibilities are dispatched as follows:

* Signal traps are set in `main`, and trigger `engine.Shutdown`
* `engine.Shutdown` coordinates cleanup by waiting for jobs to complete, and calling shutdown handlers
* To perform cleanup at shutdown, each subsystem registers handlers with `engine.OnShutdown`
* `daemon` is one subsystem, so it registers cleanup via `engine.OnShutdown`.
* `daemon` owns the pidfile, which is used to lock access to `/var/lib/docker`. Part of its cleanup is to remove the pidfile.

Signed-off-by: Solomon Hykes <solomon@docker.com>