packaging: setup: avoid confusing messages on db credentials

removed confusing message:
  Using existing credentials

If we're not asking for credentials, if we're not provisioning
it's implicit and if we're provisioning it's not true.

Change-Id: I0a83fb945c49c7c2c2b4ad49d0dbd87e42144d54
Bug-Url: https://bugzilla.redhat.com/1030829
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>