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
Print about "copy volume content" test passing

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Add maintainers to daemon/ and graph/

Signed-off-by: Solomon Hykes <solomon@docker.com>
utils/broadcastwriter -> pkg/broadcastwriter

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
utils.Debugf -> log.Printf, move jsonlog to own package.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
port usage of jsonlog to the new daemon files which were refactored
recently.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
Update CONTRIBUTING.md

Added link to community guidelines
Make it clear that JSON array format should be used if CMD is used as default arguments

Signed-off-by: Xuecong Liao <satorulogic@gmail.com>
Only import "testing" from *_test.go

This prevents the testing package flags from leaking into the flagsets
of binaries that import docker. I left integration-cli alone.

Docker-DCO-1.1-Signed-off-by: Peter Bourgon <peter@bourgon.org> (github: peterbourgon)
Run hack/generate-authors.sh

Docker-DCO-1.1-Signed-off-by: Peter Waller <p@pwaller.net> (github: pwaller)
Change Peter Waller's canonical e-mail address

Docker-DCO-1.1-Signed-off-by: Peter Waller <p@pwaller.net> (github: pwaller)
Add a few canonicalized author names

Docker-DCO-1.1-Signed-off-by: Peter Waller <p@pwaller.net> (github: pwaller)
Regenerate AUTHORS one more time

Signed-off-by: Andrew Page <admwiggin@gmail.com>
Graphtest is ok to compile normally

The graphtest package is only imported in the test files of other
packages therefore we do not leak testing flags.

Signed-off-by: Michael Crosby <michael@docker.com>
Merge pull request #7474 from crosbymichael/testing-import

Only import "testing" in test packages
Merge pull request #7329 from erikh/move_broadcastwriter

Cleanup: utils/broadcastwriter -> pkg/broadcastwriter
Merge pull request #7405 from LK4D4/indicate_run_volume_test_pass

Print about "copy volume content" test passing