--help option and help command should print to stdout not stderr

--help and help are successfull commands so output should not go to error.

QE teams have requested this change, also users doing docker help | less
or docker run --help | less would expect this to work.

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

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
Docker should use /var/tmp for large temporary files.

/tmp is often a tmpfs file system and large temporary files could cause
docker commands to fail.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
Report child error better (and later)

We use a unix domain socketpair instead of a pipe for the sync pipe,
which allows us to use two-way shutdown. After sending the
context we shut down the write side which lets the child know
it finished reading.

We then block on a read in the parent for the child closing the file
(ensuring we close our version of it too) to sync for when the child
is finished initializing. If the read is non-empty we assume this
is an error report and fail with an error. Otherwise we continue as
before.

This also means we're now calling back the start callback later,
meaning at that point its more likely to have succeeded, as well as
having consumed all the container resources (like volume mounts,
making it safe to e.g. unmount them when the start callback is
called).

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

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: rhatdan)
Allow setting of environment variables when importing docker images

We want to be able to set the container=docker environment
variable when we build RHEL docker images.  I believe there
will be other use cases where you might want to set
environment in base images.

Since you can do this in layered image, I see no reason not
to allow it in base images.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
Save "COMMENT" field in Dockerfile into image content.

This will allow a user to save COMMENT data into an image, which
can later be retrieved using:

docker inspect IMAGEID

Copied the test example and some description data from Erik Hollensbe
<github@hollensbe.org>

Add support to allow docker import to populate Comment field

This patch also adds an option to docker import -m  Which will allow
base image builder to populate docker images with more comments then
just imported from FOOBAR.  This matches the docker commit -m functionality.

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

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

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

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
Clear all capabilities even those that do not exist in capabilities.go

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

Something like access to a UUID, for containers.
https://github.com/dotcloud/docker/issues/3506

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)

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