pkg/reexec: move reexec code to a new package

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
doc: Update host integration article

Update for changes in docker 1.2. Running the docker daemon with "-r=false" has been deprecated in favor of per-container restart policies.

Signed-off-by: wilsaj <wilson.andrew.j+github@gmail.com>
Merge pull request #8856 from unclejack/reexec_pkg

pkg/reexec: move reexec code to a new package
Merge pull request #8822 from wilsaj/patch-2

Update host integration article
Add missing code example to RM command

* The command to delete all stopped containers is described, but not shown.
* Signed-off-by: John Dowd <dowdjj@gmail.com>