authentication information per image

[c-erb]

Added the possibility to define user and password information per image. It will also hide the secret information now in the logs. I wrote it backwards compatible, so if the container_image_list is still a list and not in the new dictionary format, then it will be created as a dictionary and used internally. The variables container_image_user and container_image_password will be used as a default value now if they are defined and if the image has no other authentication information defined.

[c-erb]

This is useful and needed if you have the containers in docker hub and on github as packages for example.

[ikke-t]

thanks for the neat feature, and sorry for the late response!