ENH: log ERROR with information about impl whenever specification is incorrectly specified
ENH: log ERROR with information about impl whenever specification is incorrectly specified

now it would look like

$> neurodocker generate singularity --base debian:stretch --pkg-manager apt --neurodebian datalad
[NEURODOCKER 2018-08-03 14:10:40,223 ERROR]: Failed to instantiate <class neurodocker.interfaces.interfaces.NeuroDebian>: __init__() missing 2 required positional arguments: os_codename and server
Traceback (most recent call last):
  File "/home/yoh/proj/repronim/neurodocker/venvs/dev3/bin/neurodocker", line 11, in <module>
    load_entry_point(neurodocker, console_scripts, neurodocker)()
  File "/home/yoh/proj/repronim/neurodocker/neurodocker/neurodocker.py", line 340, in main
    subparser_functions[namespace.subsubparser_name](namespace)
  File "/home/yoh/proj/repronim/neurodocker/neurodocker/neurodocker.py", line 293, in generate
    print(recipe_obj.render())
  File "/home/yoh/proj/repronim/neurodocker/neurodocker/generators/singularity.py", line 117, in render
    self._fill_parts()
  File "/home/yoh/proj/repronim/neurodocker/neurodocker/generators/singularity.py", line 168, in _fill_parts
    interface = impl(pkg_manager=pkg_man, **params)
TypeError: __init__() missing 2 required positional arguments: os_codename and server

So I would know that it was NeuroDebian specification which was wrong.
I on purpose avoided swalling/rethrowing another exception here so debugging
"on failure" could still get to the heart of the exception (which would not be
the case if I thrown a new one)

kaczmarj/neurodocker,kaczmarj/neurodocker