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