The backend will figure out if we have the image or not, otherwise will
atempt to pull if not there.
Skip retrieve integration test with img as its not supported.
This changeset also drops --keep-exported-images, which is quite unused
and can be replaced with a plugin, or either by manually exporting the
resulting images.
Is it more faster in this way as we already have all the needed folders
to the comparison extracted. In this way we don't repeat I/O operation
twice by calling container-diff.
Do not depend on container-diff anymore
