In some situations, like when a docker compose file use a data volume
to persist postgresql databases, the Odoo server starts and tries to
connect to database server before the postgresql server is ready.
In such a case, the Odoo containers fails to start.
With this commit, the wait-for-it script is used to wait for the
database server service to be ready before starting Odoo.
This script is available as a Debian package.
Closes#258, closes#259
