Added proposed Docker Community Guidelines

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
Update nodejs_web_app.md

The image centos:centos6.4 doesn't exist. Instead you have to choose between the official centos6 or centos7. Both images does not work together with de yum npm install. When choosing an centos6.5 from another distributor (tutum) it works.
integcli: add some more docker utils

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
integcli: use dockerCmdInDir in build tests

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Update nodejs_web_app.md

Updated to documentation to use the centos6 image instead of the unofficial tutum image of centos6.4
networking.md: Networking between containers works without ip_forward

Docker-DCO-1.1-Signed-off-by: Erik Inge Bolsø <knan@redpill-linpro.com> (github: knan-linpro)
Remove redundant checks in runconfig.Merge

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Cleanup Cmd on ENTRYPOINT instruction

Fixes #5147
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Inherit Cmd only if no --entrypoint specified on run

Fixes #5147
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Print about "copy volume content" test passing

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Added "Github Submodules" section to Automated Builds doc.

Signed-off-by: Hollie Teal <hollie.teal@docker.com>
Correct grammer in MAINTAINERS.md

Signed-off-by: Stephen Crosby <stevecrozz@gmail.com>
Add a "daemon" build tag and toggle it with the already-existing "DOCKER_CLIENTONLY" build variable

This works mostly by refactoring our "main" package to be careful about what it imports based on the daemon build tag. :)

Also, I've updated Travis to test "client-only" compilation after it tests the daemon version.

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Adjust build tags to be client-only in "make cross" too

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #7310 from stevecrozz/maintainers-grammar-update

Correct grammar in MAINTAINERS.md
Merge pull request #7377 from tianon/daemon-build-tag

Add a "daemon" build tag and toggle it with the already-existing "DOCKER_CLIENTONLY" build variable
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)
Merge pull request #7349 from knan-linpro/master

networking.md: Networking between containers works without ip_forward
Add contrib/nuke-graph-directory.sh script to clean out old /var/lib/docker directories much more easily

Signed-off-by: Andrew Page <admwiggin@gmail.com>
Merge pull request #6909 from LK4D4/prune_cmd_on_entrypoint_setting_#5147

Cleanup cmd on entrypoint setting