registry: make certain headers optional

For a pull-only, static registry, there only a couple of headers that
need to be optional (that are presently required.
* X-Docker-Registry-Version
* X-Docker-Size
* X-Docker-Endpoints

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
registry: Info collection

roll version and standalone information into the _ping. And to support
Headers they are checked after the JSON is loaded (if there is anything
to load). To stay backwards compatible, if the _ping contents are not
able to unmarshal to RegistryInfo, do not stop, but continue with the
same behavior.

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Added support for multiple endpoints in X-Docker-Endpoints header
Docker-DCO-1.1-Signed-off-by: Joffrey F <joffrey@docker.com> (github: shin-)
typo fix: 'methid' -> 'method'
container: Remove Ghost state

container.Register() checks both IsRunning() and IsGhost(), but at
this point IsGhost() is always true if IsRunning() is true. For a
newly created container both are false, and for a restored-from-disk
container Daemon.load() sets Ghost to true if IsRunning is true. So we
just drop the IsGhost check.

This was the last call to IsGhost, so we remove It and all other
traces of the ghost state.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Move "possible config locations" list to the top of check-config.sh

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Update contributed man page file names and compilation script for the eventual possibility of non-man1 man pages (hopefully a Dockerfile.5.md, for example)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
engine.Installer: a standard interface for "installable" services

Installer is a standard interface for objects which can "install"
themselves an engine by registering handlers.

This can be used as an entrypoint for external plugins etc.

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
don't try allocating a port to upload a docs release to s3

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Remove the concept of a root dir out of engine

This makes the engine more general purpose so that we can
use it and the job routing functionality for reexec'ing our binary
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

Conflicts:
	integration/runtime_test.go
Merge pull request #5346 from SvenDowideit/dont-alocate-port-for-docs-release

Remove port allocation from `make docs-release`
Update tests with engine root removal
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Fixed an missing '-' on the "--rm"

Docker-DCO-1.1-Signed-off-by: William Henry <whenry@redhat.com> (github: ipbabble)

 Changes to be committed:
	modified:   contrib/man/md/docker-build.md
Merge branch 'man1-assumption' of https://github.com/tianon/docker into manpages
Fixed some missing ']' and the TAG

Docker-DCO-1.1-Signed-off-by: William Henry <whenry@redhat.com> (github: ipbabble)

 Changes to be committed:
	modified:   contrib/man/md/docker-build.1.md
fixed broken link to chef community site
Merge pull request #5352 from rmoriz/patch-1

Merged.
Development docs warning for beta-docs.docker.io

Update: Fix alignment issues of the "warning" block.

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

Docker-DCO-1.1-Signed-off-by: O.S.Tezer <ostezer@gmail.com> (github: SvenDowideit)
make the non-release doc warning conditional and add version info

use the beta-warning area to tell the user what VERSION of docker, git
branch, and links to the official release version docs are.

requires / extends PR #5272

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Merge pull request #5337 from tianon/man1-assumption

Update contributed man page file names and compilation script