Add postgresql to the default of notification_service_id option

[Peter Stachowski]

The option 'notification_service_id' has a default value for all supported databases, except postgresql. This should be added.

[Auston McReynolds (amcrn)]

i had this issue pointed out on https://review.openstack.org/#/c/57609/15/trove/common/cfg.py too... looks like we missed it.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/123588

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/123588
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=df7332e72f4422b0afb49a17cb02d843e11354c5
Submitter: Jenkins
Branch: master

commit df7332e72f4422b0afb49a17cb02d843e11354c5
Author: Peter Stachowski <email address hidden>
Date: Sat Sep 20 22:34:07 2014 -0400

    Add postgresql to notification_service_id option

    The Trove 'notification_service_id' option has a default value for all
    supported databases, except postgresql.

    PostgreSQL now has a default value as well.

    Change-Id: I033884bc36ba4ffe3faaf6cc4e3496cfb757858b
    Closes-Bug: #1373083