Fix inherit output separate

Pull req https://github.com/autotest/autotest-docker/pull/393 should be applied before this pullreq.

Based on pull req https://github.com/autotest/autotest-docker/pull/352.
I was try to split what was possible but rest of splitting is time very expensive and could lead
to more problems. I want avoid this.

Simplifies docker interface mechanism from object composition to
module global variable assignation.
Adds variables in defaults.ini to set default test interface.

default_container_iface = cli
default_images_iface = cli
default_dockercmd_iface = cli

example how to change default interface in whole test:
module global variable DockerImages

images.DockerImage = new interface class.

move cmd output check to OutputCheck module

separate subsubtests from each other more precisely.