Support TRYTOND_DATABASE_URI as database basis for scripts
When using the Docker images to run those scripts, the environment variable TRYTOND_DATABASE_URI can not be used because the database option is required.
Indeed if the user set only a database name, we should use the URI to construct the proper parameter. So it will allow to run script like:
docker run --rm -ti tryton/tryton trytond_import_currencies -d
This unify the usage with other command line like trytond-cron etc.