scheduler_driver option can't be clean up

[Xingchao Yu]

in current logic, scheduler_driver option can't be clean up even we set its value to false.
Add a else logic will solve this problem.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/167088

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/167088
Committed: https://git.openstack.org/cgit/stackforge/puppet-cinder/commit/?id=54d77c27ae0725e91165ab9d26f87a9c56ba4d2b
Submitter: Jenkins
Branch: master

commit 54d77c27ae0725e91165ab9d26f87a9c56ba4d2b
Author: Xingchao Yu <email address hidden>
Date: Tue Mar 24 12:24:30 2015 +0800

    Make scheduler_driver option can be clean up

    Current, scheduler_driver option can't be cleaned up even we set it
    to false. This patch just add ELSE logic to fix it.

    Closes-Bug: #1435660
    Change-Id: I7d4634f2e99a025cfde317fc2eb1240a81824803