Using Conan for dependency resolution has broken README.md generation

[jfpanisset]

Since switching to using Conan to figure out at runtime which packages need to be included in a ci-XXXX image and removing
the static list from ci-XXXX/image.yaml, generation by aswfdocker dockergen of the ci-XXXX/README.md no longer works:

• dependencies are no longer listed
• the package itself is incorrectly listed as included

It should be possible to call:

conan info . --only requires

to get this list, but this has to be done in the context of a container which includes Conan itself.