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: I1c74518db882fe91955a69132e8fb5d4cd212329
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>