packaging: setup: hardening postgresql password

Use random.SystemRandom instead of random and
extend password lenght to 22 chars in order to have at least 128 bits of entropy.

Change-Id: I76769e7eb65df35f982b1ef9e36bc81d1f42b79a
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>
(cherry picked from commit 78d5316978a2a078683819a94891d09d403d46b0)