Fix handling of the ironbank base container

[dirkmueller]

The ironbank base container is a fips container but actually called bci-base.

[dcermak]

Would it maybe make the handling a bit simpler if we added bci-base to BASE_FIPS_CONTAINERS if the target is "dso"?

[dirkmueller]

Would it maybe make the handling a bit simpler if we added bci-base to BASE_FIPS_CONTAINERS if the target is "dso"?

not really, because we expect BASE_CONTAINER to be always existing and exactly one container everywhere. I've pushed an additional commit to do what you're asking for. I think the previous solution was simpler.