do not alter json in docker save

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
improve test

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
add a test using the flags

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
More verbose error for parallel pull

Partially fixes #6484
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Validate that one of streams choosen in logs on api side

Fixes #6506

There is the bug, that very hard to fix: When we return job.Errorf in
"logs" job it writes to job.Stderr, to which connected ResponseWriter and on
this write w.WriteHeader(http.StatusOK) is called. So, we get 200 on error
from "logs" job.

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
docker save: raw json

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Merge pull request #6503 from LK4D4/verbose_parallel_error_pull_#6484

More verbose error for parallel pull
Merge pull request #6516 from LK4D4/validate_logs_params

Validate that one of streams choosen in logs on api side
Merge pull request #6571 from vbatts/vbatts-raw_json

raw json for `docker save`