To make it short: It works now.
I wanted to use python gvm-tools, but never got it running properly without a virtualenv.
After you said that under version 1.7 it should be possible to install packages which requires python3, i got curious.
I updated pip, installed gvm-tools again and suddenly it gave me a warning which PATH i have to add to get it running… and finally it works.
Thank you, and forgive me for my bad linux skills