Support creating of "hollow" runtime images

[gunnarmorling]

Similar to "hollow uber JARs" in WildFly Swarm it should be possible to create hollow runtime images.

Such image would only contain an application's dependencies, whereas the appliciation module(s) themselves would be added only at execution time via --module-path. That'd be desirable for usage with Docker, where one could have one image with the (relatively stable) application dependencies and another one with the (more frequently changing) application modules which can be much smaller that way.