Assert deep equality (and provide useful difference as a test failure).

Assert the simplistic pointer (or literal value) equality.

DockerRunAndCopy runs a container and once stopped, outputCtrPath is copied to outputDir.

DockerRunWithError allows to run docker command that might fail, reporting the error back to the caller.

DockerSeedRunAndCopy copies srcDir to container's srcCtrPath before container is started.

FIXME: re-work this function to exec the docker cli, or convert other docker helpers to using the client library.

SeedDockerVolume only works with Linux daemons.