Re-create images for all builders

The fix deployed for MDBF-34 and which solved MDBF-35 requires enabling 'utf-8' encoding for the buildbot workers. This happens during the docker image creation. Because of this, all the images need to be re-created (docker is using the cached old ones and does not re-create them automatically).

This is also a good opportunity to update the python version to python3 since buildbot no longer supports python2.