When sending a new job to a `engine.Sender`, the corresponding
`engine.Receiver` will receive that job with its environment preserved.
Previously the job name, arguments and streams were preserved but the
env was lost.
Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Upstream-commit: a1754c7e46b321c2a079fc5186984a847aa50218
Component: engine