To avoid a zombie apocalypse, use cmd.Wait() to properly finish
the processes we spawn by Start().
Found while investigating DockerSuite.TestLogsFollowSlowStdoutConsumer
failure on ARM (see
https://github.com/moby/moby/pull/34550#issuecomment-324937936).
[v2: don't expect no error from Wait() when process is killed]
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Upstream-commit: 14f0a1888f92667f82bea548bfa2fe4a890a75e8
Component: engine