docs: explain DNS warnings & how to fix them

This explains how to fix the DNS warnings on Ubuntu and why they're
shown.

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
forbid chained onbuild, from & maintainer triggers

This changes the way onbuild works:
- forbids the chaining of onbuild instructions
- forbids the use of `onbuild from`
- forbids the use of `onbuild maintainer`

It also makes docker throw errors when encountering such triggers when
executing the triggers during `FROM`.

Three tests have been added:
- ensure that chained onbuild (`onbuild onbuild`) is forbidden
- ensure that `onbuild from` is forbidden
- ensure that `onbuild maintainer` is forbidden

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Merge pull request #3845 from alexlarsson/tar-caps

Implement capabilitiy bit storage in layers
Fix registry auth by storing the string passed on the command line, and allowing for credential selection by normalizing on hostname. Also, remove remote ping calls from CmdPush and CmdPull.

Docker-DCO-1.1-Signed-off-by: Jake Moshenko <jake@devtable.com> (github: jakedt)
Fix build command auth by adding the auth config and registry objects to the build job environment.

Docker-DCO-1.1-Signed-off-by: Jake Moshenko <jake@devtable.com> (github: jakedt)
Merge pull request #4265 from unclejack/explain_networkmanager_and_dns_problems

docs: explain DNS warnings & how to fix them
Merge pull request #4252 from SvenDowideit/mention-scratch-image

lets talk about the other way to make base images
Merge pull request #4261 from amouat/patch-1

Fix misspelling
Merge pull request #4251 from tianon/add-back-grub-info

Add back the Ubuntu "Memory and Swap Accounting" section that was lost when the "Kernel" page was culled
Merge pull request #4233 from deedubs/patch-1

FIX: Linux mint troubleshooting tip
reinforce that docker build --rm is a good default to use

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Merge pull request #4273 from SvenDowideit/docker-build-rm

reinforce that docker build --rm is a good default to use
Add newlines to the JSON stream functions

This makes the JSON streams a _lot_ easier to parse in less well-baked JSON parsers, and no less so in better ones.

Line-based JSON streams are very, very common, where simply chunk-based is not very common at all.

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
small update to API docs to go with #4276

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Add MTU to lxc conf to make host and container MTU match

If you are using jumbo frames the host side of the veth was being set to
1500.  Docker would set the MTU of the container side of the veth to 9001.
This would lead to a situation in which the two sides of the veth had
different MTU sizes causing issues in network traffic.

Docker-DCO-1.1-Signed-off-by: Darren Shepherd <darren.s.shepherd@gmail.com> (github: ibuildthecloud)
Merge pull request #4248 from unclejack/https_fixes

don't skip cert check for an example & use HTTPS
Fix cli argument usage typo for docker --mtu

Docker-DCO-1.1-Signed-off-by: Danny Berger <dpb587@gmail.com> (github: dpb587)
Merge pull request #4260 from unclejack/onbuild_fixes

forbid chained onbuild, from & maintainer triggers
Merge pull request #4271 from DevTable/fixbuildauth

Fix build auth by adding config to the build job environment
docs: document some JSON parameters /containers/create and /containers/(id)/start in remote api (fixes #2948)

Docker-DCO-1.1-Signed-off-by: Manuel Woelker <github@manuel.woelker.org> (github: manuel-woelker)