Add fake_cgsnapshot for cinder unittest

[Peter Wang]

Since all cinder objects have been converted to objects, fake objects are needed during UT, many fake objects are provided such as fake volume, fake snapshot, fake consistency group. So it's necessary to generate fake cgsnapshot object for UT as well
Without this change, third party driver could not use cgsnapshot like below:

cgsnapshot.id
cgsnapshot.consistencygroup

Thanks
Peter

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/299297

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/299297
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=0e5e631087257c1ee18f1d34ff2b03b1e88f9f0c
Submitter: Jenkins
Branch: master

commit 0e5e631087257c1ee18f1d34ff2b03b1e88f9f0c
Author: Peter Wang <email address hidden>
Date: Wed Mar 30 16:53:08 2016 +0800

    Add fake_cgsnapshot for unittest use

    This patch add the missing fake object generator
    for CG snapshot.

    Change-Id: Ifee32b2d649d6a37813d116ac981cd89aeb52237
    Cloese-bug: #1563770