If service name is not passed, set it to an empty string

[Lin Hua Cheng]

When no service name is passed to the API, set the service name to empty string before passing to database or driver.

This is a follow-up on the suggestion made in:

https://review.openstack.org/#/c/135808/9/keystone/catalog/backends/sql.py

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/146962

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/146962
Committed: https://git.openstack.org/cgit/openstack/keystone/commit/?id=cc54a6ee48474ccb5ebbf2746e960a4b71c96e48
Submitter: Jenkins
Branch: master

commit cc54a6ee48474ccb5ebbf2746e960a4b71c96e48
Author: lin-hua-cheng <email address hidden>
Date: Tue Jan 13 11:30:42 2015 -0800

    On creation default service name to empty string

    To make new data consistent with existing data, this include a data
    migration script to default the service name to empty string as well.

    Change-Id: I1b5fd5fbf08939c3bdc29298c77f1f11aec07a29
    Closes-Bug: #1410389