Can't override a private method like this.  Better to either make the super-class method non-private and part of the interface, or come up with a different way...

...since this concept is specific to the CLI interface, how about make a ``DockerContainersCLI.ps_args`` class attribute or property?.  We like things fast by default, so I think it's okay to drop the ``--speed``  (TBH, I dunno why I put it there anyway).  Anyhoo, this way, if a caller or subclass wants to extend this (hint hint as in "args" param above) it's right there for the taking.