packaging: setup: clear PGPASSWORD when interacting with database

when both PGPASSWORD and PGPASSFILE are specified the PGPASSWORD takes
precedence, so we should unset/zero it to avoid errors when user has
PGPASSWORD within environment and executes setup.

Change-Id: Ie02939fe51eb4308d76a65e9eb1eb86df4a6801c
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>