fix get_user_display_name on docker

[leo-schick]

On docker the flask mara_pipelines.ui.run-interactively fails with

This is a fix for this: According to the python documentation os.getlogin(), getpass.getuser() should be used.

[jankatins]

Does that work in the end in the environment where os.getlogin() failed?

[jankatins]

Maybe also wrap it in a try/except in case this ends up with the same problem? Haven't looks into what getuser does internally...

[leo-schick]

Done.