This adds a new `imageStream` option that can be used in conjunction
with `pkgs.dockerTools.streamLayeredImage` so that the image archive
never needs to be materialized in the `/nix/store`. This greatly
improves the disk utilization for systems that use container images
built using Nix because they only need to store image layers instead of
the full image. Additionally, when deploying the new system and only
new layers need to be built/copied.
The cntr sometimes hangs until the 10-hour hydra limit. This behaviour
appears to be an edge-case related to the type of TTY in which the cntr
command runs during test execution. We can work around this by running
the command as a background job.
I additionally added a wait_for_open_port to fix nondeterministic test
failures I observed after fixing the hanging issue.
