extend volume for LVM got lost in the shuffle

[John Griffith]

The extend volume method was proposed for the reference LVM implementation but somewhere along the way got lost and we just realized that it wasn't put in place. This is a simple add and should definitely be in place for the reference driver impl.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/47638

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/47638
Committed: http://github.com/openstack/cinder/commit/966a514821738caf7835e7781037a04454e3299d
Submitter: Jenkins
Branch: master

commit 966a514821738caf7835e7781037a04454e3299d
Author: John Griffith <email address hidden>
Date: Fri Sep 20 21:30:36 2013 +0000

    Add extend to reference LVM driver

    Somwhere along the way we somehow dropped
    or missed implementing the extend functionality
    in the reference LVM driver.

    Add it.

    Change-Id: Ib3efe16252b5efacce253688767df426117b2a44
    Closes-Bug: #1228358