Though it's perfectly valid to subclass around behaviours (as you have done), but I smell trouble down the road.  In fact, now I think it was my mistake to add ``DockerContainersCLICheck``.  That could easily just use a boolean instance attribute instead.  Otherwise, if we keep extending this way (where the subclasses are very-narrowly "different")  I think the main ``DockerContainers.interfaces`` map will quickly become unwieldy.  In other words, we should probably reserve that just for example 'cli' vs 'rest' and such.

I'll make myself a note to nuke ``DockerContainersCLICheck`` and fix the tests that use it (in next major version).