Possibility to define in fig.yml if container should be created or not

[vidarl]

There are use-cases where you want to create base images ( which you'll use for creating other images ), but you don't need any containers from those images.

There are also use-cases where you want containers to be created, but purged once they ends ( like docker run --rm ... )

This could be configurable with the following syntax:

ubuntu:
  build: dockerfiles/ubuntu
  create_container: false # true is default
foobar:
  build: dockerfiles/foobar
  remove_container: true # false is default

[dnephin]

Duplicate of #1896