Add a few small tweaks to mkimage-debootstrap, especially to help with lucid

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
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)
Added new mkimage-yum.sh script to create CentOS base images

mkimage-rinse.sh requires rinse, which is not readily available on
CentOS or Fedora.  Plus, creating a base image is trivial with yum
alone.

Docker-DCO-1.1-Signed-off-by: Chris St. Pierre <chris.a.st.pierre@gmail.com> (github: stpierre)
fix shebang in mkimage-yum.sh

Docker-DCO-1.1-Signed-off-by: Chris St. Pierre <chris.a.st.pierre@gmail.com> (github: stpierre)
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)
execdriver: Make GetPidsForContainer() a driver call

The current implementation is lxc specific.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
network: add publicly mapped ports to FORWARD table

Allow publicly mapped ports to be made public beyond the host.  This is
needed for distros like Fedora and RHEL which have a reject all rule at
the end of their FORWARD table.

Docker-DCO-1.1-Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> (github: jpoimboe)
docs: remove ip_forward enabling step

Now that docker sets /proc/sys/net/ipv4/ip_forward by default, remove
the step to enable it in the installation docs.

Docker-DCO-1.1-Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> (github: jpoimboe)
Initial move of port mapper code into sub pkg

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
remove enableCors from the config and move it as a job arg

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Move port mapper tests out of core and into portmapper

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
move warnings to the job

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Address feedback from @jamtur01.
Docker-DCO-1.1-Signed-off-by: Andy Rothfusz <github@developersupport.net> (github: metalivedev)
Merge pull request #3813 from jpoimboe/update-ip_forward-docs

docs: remove ip_forward enabling step
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)
ExecStartPre commands updated

Docker-DCO-1.1-Signed-off-by: Lokesh Mandvekar <lsm5@redhat.com> (github: lsm5)

systemd service no longer does '/bin/mount/ --make-rprivate /'.
Core issue fixed by Alex Larsson (commit 157d99a).

ip forwarding enabled.
remove ip fowarding from systemd (fixed: commit #3801)

Docker-DCO-1.1-Signed-off-by: Lokesh Mandvekar <lsm5@redhat.com> (github: lsm5)
Merge pull request #3588 from tianon/debootstrap-tweaks

Add a few small tweaks to mkimage-debootstrap, especially to help with lucid