Don't shell out to tar for ExportChanges

This changes ExportChanges to use the go tar support so we can
directly create tar layer files. This has several advantages:

* We don't have to create the whiteout files on disk to get them
  added to the layer

* We can later guarantee specific features (such as xattrs) being
  supported by the tar implementation.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Fix cross compile

stat.Rdev and time.* is 32bit on OSX, which breaks cross builds with eg:
cannot use stat.Rdev (type int32) as type uint64 in function argument

We fix this with an extra conversion to uint64.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Fixes Issue# 3450
Docker-DCO-1.1-Signed-off-by: Gopikannan Venugopalsamy <gopikannan.venugopalsamy@gmail.com> (github: vgeta)
Fix docs manpage generation

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Add Dockerfile man page generation from our Dockerfile reference page

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Update Travis to also compile the man page(s) now that they compile properly again

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #3292 from alexlarsson/export-changes-manual

Don't shell out to tar for ExportChanges
Merge pull request #3665 from vgeta/3450-fix

Fixes Issue #3450
Fix Travis build errors by bumping our python module versions to be newer

See also https://bitbucket.org/birkenfeld/sphinx/issue/1281/sphinx-113-not-build-proper-manpages

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #3650 from tianon/fix-doc-man-generation

Fix docs man page generation and add Dockerfile man page
Merge pull request #3681 from pnasrat/extract-cgroups-pkg

Extract cgroups into pkg sub dir
Don't expose cgroups via the execdriver API.

Use Resources to represent container limits rather than a cgroup specific field.

Docker-DCO-1.1-Signed-off-by: Paul Nasrat <pnasrat@gmail.com> (github: pnasrat)