data persistence: use volumes instead of bind mounts

[pilou-]

According to the docker documentation:

Volumes are the preferred way to persist data in Docker containers and services.

Then there is no need to import /var/log/postgresql/9.5 from archive (doc):

If you mount an empty volume into a directory in the container in which files or directories exist, these files or directories will be propagated (copied) into the volume.

[frankrousseau]

Great ! Thank you