Fails to work with updated gsm

[jmsaurel]

A new gsm version has been published in May.
Docker creation fails at step 10 (step 9 that install SeisComP is probably failing before).

[jmsaurel]

Gsm now uses python3-venv to isolate a working environment.
Issue should be solve by PR #4

[PBoissier]

PR merged, I close the issue