Change I380dd20e5ed716a0bdf92aa02c3730359b8136e4 updated the tempest
configuration to stop creating a bunch of globals. But as part of
that refactor it started using $admin_password as the password
argument for tempest-account generator, which is never defined.
This commit rectifies the situation by using the correct variable
$password.
Change-Id: Ieeed58751e5784020e04bcc2911ac74791662110