input/output default dirs

[chbrandt]

System considers two default (or mandatory) directories to communicate with containers: input and output. Their "default" existence should be reconsidered, because they can be (very) welcome for my (chbrandt) own images, but not for third-party ones.

Consider the gollum image, the image is setup to use (internally) the /wiki dir; and that is all it needs. So, to add input/output dirs is unnecessary (and ugly).