The option `--allow-missing-files` is not propagated to all toolchain elements

I think we must propagate --allow-missing-files options to all elements in our base toolchain.

One way to do that is to work this out in this function https://gitlab.idiap.ch/bob/bob.bio.base/blob/54be30749e89a1e99a7fb267787d81ea4e053314/bob/bio/base/utils/io.py#L178

Related with bob.bio.gmm#21 (closed)