Fix NameErrors in ci base-build and ci test commands

You can see the code failing in https://gitlab.idiap.ch/bob/bob.conda/-/jobs/170227

@andre.anjos could you run black (https://github.com/psf/black) on all the files in this repository? I don't want to do it myself since you have written most files.

merged

mentioned in commit 5094e683

I added black as a dependence for this package, so you get this tool by default when you install/update bdt.

To consistently apply black everywhere, we need to agree on a few things:

1. Shall we be using 80-column (ANSI) standard widths?
2. Shall we format code with target py36 at least?
3. This bug on docstring formatting is still opened: https://github.com/psf/black/issues/144 (see affecting issue here: https://github.com/psf/black/issues/473). This implies you need to do a manual pass on all docstrings before you commit the changes proposed.

I added the package docformatter as a dependence to bdt as well. With that, it is possible to reformat code and get a reasonable overall output.

The rule is to pass black followed by docformatter.

I also committed the cleaned-up code back (see !89 (merged)).