Fix the passwords generation precedence for containerized UC and
standalone installations. This allows users to provide custom
passwords/secrets in tripleo-undercloud-passwords.yaml, or
undercloud-passwords.conf, when upgrading from instack.
Partial-bug: #1784576
Change-Id: If7166c2419794dd9595d25ad29ee1fdafce99d72
Signed-off-by: Bogdan Dobrelya <bdobreli@redhat.com>