Previously, ``_set_db_params`` would be called several times and
parameters would then be concatenated. We didn't want
``_set_db_params`` to overwrite and start from scratch to let
possibility for customization before and after the call.
Here ``set_db_params`` will set a global variable to detect if it was
already launched prior to running content of ``_set_db_params``.
Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>