Provide an alternative way to create volume from snapshot or volume in VNX Cinder driver

[Xi Yang]

Currently in VNX Cinder driver, a full-copy will be performed when creating a volume from snapshot or volume. This is time-consuming.
In order to address this issue, VNX Cinder driver can provide an alternative way which is performing a snap-copy when creating a volume from snapshot or volume. This can accelerate the proccess a lot. And if the user wants to perform a full-copy on the snap -copy volume, he can trigger migration or retype on it.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/184733

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/184733
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=afbaf3d2f103edaef44901a405f4d9cfaecd50bc
Submitter: Jenkins
Branch: master

commit afbaf3d2f103edaef44901a405f4d9cfaecd50bc
Author: Xi Yang <email address hidden>
Date: Thu May 21 04:09:21 2015 -0400

    Snap copy feature for EMC VNX Cinder driver

    Currently in VNX Cinder driver, a full-copy will be performed
    when creating a volume from snapshot or volume and it is
    time-consuming. This patch is going to address this issue by
    providing an alternative way which is performing a snap-copy
    when creating a volume from snapshot or volume. This can
    accelerate the proccess a lot. And if the user wants to perform
    a full-copy on the snap-copy volume, migration or retype can be
    triggered on it. And we implement update_migrated_volume to
    support migration and retype on the snap-copy volume.

    DocImpact
    Change-Id: I134a2d2274b1e3b85ea08cbf5e034f47d98e97db
    Closes-Bug: #1457274