Update hack/dind to mount cgroups on "/cgroup" instead of "/sys/fs/cgroup" for better compatibility

Fixes #5122

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Introduce x-axe scrolling to code-blocks.

This improvement introduces x-axe scrolling to code-blocks by
overriding certain default bootstrap word-wrapping constraints.

This PR closes: https://github.com/dotcloud/docker/issues/5279

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)
Add code for Pardot implementation to docs

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)
registry: adding vbatts to the MAINTAINERS

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Cast Input and Output to closer
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Rewrite and update the MongoDB service article

MongoDB article had some fundemental issues.

 - Outdated Dockerfile
 - Insufficient / unclear instructions
 - Unnecessary comments
 - Failed to explain the role of Docker.io
 - Did not have a complete Dockerfile sample
 - Lacked a "learn more" section / link to Trusted Builds

This update aims to address all these issues with a complete re-write.

It also:

 - Corrects the label under which this article is/was listed on the menu

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)

 - First run at amending after the initial review process.
 - Make the Dockerfile generic.
 - Revision.
 - Fixes
Merge pull request #5599 from ostezer/docs-rewrite-examples-mongodb

Rewrite and update the MongoDB service article
Merge pull request #5583 from ostezer/docs-ui-add-codeblock-scrolling

Introduce x-axe scrolling to code-blocks.
Added value format description for VOLUME instruction

In the documentation was not mentioned explicitly that VOLUME value
shoud be a valid JSON array. Because of this I spent time to discovering
the problem with my image where I put `VOLUME ['/data']` (with single quotes).
The `['/data']` mount point was parsed and mounted whole as a string without
any errors and warnings.

Docker-DCO-1.1-Signed-off-by: Max Shytikov <mshytikov@gmail.com> (github: mshytikov)
Merge pull request #5697 from mshytikov/fix/doc

Added value format description for VOLUME instruction in builder doc
Merge pull request #5686 from crosbymichael/cast-to-closer

Cast Input and Output to io.Closer
Merge pull request #5463 from tianon/hack-dind-cgroup

Update hack/dind to mount cgroups on "/cgroup" instead of "/sys/fs/cgroup" for better compatibility
returns an error when using -h and --net

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
Merge pull request #5709 from vieux/conflict_h_net

returns an error when using -h and --net
fix event removal

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
Fix stdin handling in engine.Sender and engine.Receiver

This introduces a superficial change to the Beam API:

* `beam.SendPipe` is renamed to the more accurate `beam.SendRPipe`
* `beam.SendWPipe` is introduced as a mirror to `SendRPipe`

There is no other change in the beam API.

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Engine: fix a timeout bug in Sender/Receiver

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Engine: slightly more stress-testing of Receiver/Sender to reproduce the hang problem

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Merge pull request #5687 from shykes/pr_out_engine_fix_a_timeout_bug_in_sender_receiver
Engine: ensure all pipes are properly closed by Receiver and Sender

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)

[michael@docker.com: fix stdin closing in engine.Job.Run]
[michael@docker.com: fix fd leak in engine.Receiver.Run]
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)

Docker-Tested-By: Solomon Hykes <solomon@docker.com>
Docker-Tested-by: Michael Crosby <michael@docker.com>