Add proper support for relative WORKDIR instructions

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Improve WORKDIR test to cover more edge cases

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Add some documentation about relative WORKDIR values

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #4691 from tianon/relative-workdir

Add proper support for relative WORKDIR instructions
images: assurance and debug info on image layers

when pushing or saving layers, report sizes for validation. And ensure
that the files written are sync'ed.

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Merge pull request #4777 from vbatts/vbatts-server-info_and_assurance

images: assurance and debug info on image layers