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)
Move UserLookup functionality into a separate pkg/user submodule that implements proper parsing of /etc/passwd and /etc/group, and use that to add support for "docker run -u user:group" and for getting supplementary groups (if ":group" is not specified)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Use type switch instead of reflection

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Consolidate a bunch of the supplementary-groups tests to cut down on the number of RUN lines in a single Dockerfile within TestBuild

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

If networking is disabled, but then pipework is used later to add nics, the network still doesn't function. Using flags=up for empty networking fixes this.
Docker-DCO-1.1-Signed-off-by: James DeFelice <james.defelice@ishisystems.com> (github: jdef)
remove mention of #docker-meeting

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
docs/installation/google: remove -mtu flag
Merge pull request #3933 from proppy/patch-1

docs/installation/google: remove -mtu flag
be a little more explicit about what WORKDIR does

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Merge branch 'release' into merge_release_v0.8.0

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Change version to v0.8.0-dev
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Merge pull request #3941 from crosbymichael/merge_release_v0.8.0

Merge release v0.8.0
Fix bad rebase where bridgeiface was removed
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
devmapper: Rename DeviceSet.RemoveDevice to DeleteDevice

"Remove" is a bit overloaded, as it is also what deactivating a
device mapper device is called. Using "delete" is more clear here.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
devmapper: add and use removeDeviceAndWait helper

This adds a function that calls the lowlevel removeDevice
and then waits for it to finish.

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

Docker-DCO-1.1-Signed-off-by: Joe Shaw <joe@joeshaw.org> (github: joeshaw)
Merge pull request #3938 from SvenDowideit/workdir-doc-tweak

be a little more explicit about what WORKDIR does
Merge pull request #3944 from joeshaw/patch-1

Always download things over https
Added installation docs for CRUX as a Docker Host.

Docker-DCO-1.1-Signed-off-by: James Mills <prologic@shortcircuit.net.au> (github: therealprologic)
Do not ping registry from the cli
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)