Add experimenta btrfs driver

This is an experimental btrfs driver. To use it you must have
/var/lib/docker mounted on a btrfs filesystem and explicitly
specify DOCKER_DRIVER=btrfs in the docker daemon environment.

It works by using subvolumes for the docker image/container layers.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Update hack/make.sh with slightly clearer output and a more precise "are we in the Docker container?" check

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Fix 2720 -- Expanded documentation for docker run.
Docker-DCO-1.1-Signed-off-by: Andy Rothfusz <github@developersupport.net> (github: metalivedev)
btrfs: Add comment to Put()

Document why we don't need to do anything in Put().

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
fix(CONTRIBUTING): Developer Certificate of Origin w/o Grant

In 7fb55f77250a9b52b0515a7e655ecc605ae452ca the DCO lost the grant so
change the title back to just DCO.

Docker-DCO-1.1-Signed-off-by: Brandon Philips <brandon.philips@coreos.com> (github: philips)
Address feedback from @jamtur01.
Docker-DCO-1.1-Signed-off-by: Andy Rothfusz <github@developersupport.net> (github: metalivedev)
Make get.docker.io install directions slightly better by telling user exactly how to add themselves to the "docker" group

As a bonus, if the user has run this script the way we recommend (ie, without "sudo" or "su", run as their user), we can actually give them the exact command they'll need with their correct username substituted appropriately.

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Remove api_params.go

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
job.error\* now return engine.StatusErr

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
add setSubEnv and getSubEnv

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
move api to it's own package

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Add dummy "user.email" setting in our Dockerfile for smooth in-container merge commits

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
fix ID -> Id api

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
add tests

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
fix convertion issues

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Prevent Tests from creating users on Prod Index

The integration tests had previously used the environment variable
DOCKER_INDEX_URL but it was apparently removed several months ago.

Change the integration auth tests to specify the ServerAddress field
of the AuthConfig struct to use the staging deployment of the index.

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

Docker-DCO-1.1-Signed-off-by: Piergiuliano Bossi <pgbossi@gmail.com> (github: thinkingbox)
Merge pull request #3835 from thinkingbox/master

Fix typo
 Add troubleshooting for missing cgroups on mint 16 #3602

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
pkg/mount: Add "private" flag

This allows "mount --make-private" functionallity.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)