Fix the PYTHONPATH for the dev_worker_1 container
    
    When trying to create new project using API, with the `create_readme=True`
    parameter, there was an ImportError: No module named `pagure.lib`, in
    the pre-receive hook of the new project.
    
    In dev_worker_1 container the PYTHONPATH was pointing to `.`.
    The hooks were probably not being run from the workdir set in the
    Dockerfile. Now it points to `/code` and the error is gone.
    
    Merges #3944