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)
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)
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
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
Merge pull request #5336 from tianon/slightly-more-organized-check-config

Move "possible config locations" list to the top of check-config.sh
Remove error from engine.New()

Without creating a root there is no way for the engine to return an
error from the new function.
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Update link to interactive tutorial
Update link to interactive tutorial
Merge pull request #5347 from crosbymichael/engine-root

Remove root dir from engine
Merge pull request #5345 from shykes/engine-installer

engine.Installer: a standard interface for "installable" services
Merge pull request #5349 from ipbabble/manpages

Manpages - fixes and merged tianon/docker man1-assumption branch
Merge pull request #5362 from sindhus/patch-2

Update link to interactive tutorial
Docs auto-conversion fixes and MD marking and structure improvements.

 - Remove redundant chars and all errors caused by RST->MD conversion.
   e.g. [/#, /\, \<, />, etc.]
 - Fix broken inter-document links
 - Fix outbound links no-longer active or changed
 - Fix lists
 - Fix code blocks
 - Correct apostrophes
 - Replace redundant inline note marks for code with code marks
 - Fix broken image links
 - Remove non-functional title links
 - Correct broken cross-docs links
 - Improve readability

Note: This PR does not try to fix/amend:

 - Grammatical errors
 - Lexical errors
 - Linguistic-logic errors etc.

It just aims to fix main structural or conversion errors to serve as
a base for further amendments that will cover others including but
not limited to those mentioned above.

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

Update:

 - Fix backtick issues

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Looking into some broken links, I noticed that we don't need to use
relative paths, and also fixed some broken images.

There are still more todo - next PR I think :)

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)