Pure Storage driver needs to return snapshot objects for create_cgsnapshot and delete_cgsnapshot

[Thang Pham]

This bug is a placeholder to have Pure Storage driver return snapshot objects instead of snapshot dictionaries for create_cgsnapshot and delete_cgsnapshot methods. It was noted on a review comment in https://review.openstack.org/#/c/163910/14//COMMIT_MSG. This can be done be replacing occurences of db.snapshot_get_all_for_cgsnapshot() to SnapshotList.get_all_for_cgsnapshot() in create_cgsnapshot and delete_cgsnapshot. It is dependent on https://review.openstack.org/#/c/163910/.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/211802

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/211802
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=863d3456c6a4667d68f27ebb759f1adbf8f6f3ea
Submitter: Jenkins
Branch: master

commit 863d3456c6a4667d68f27ebb759f1adbf8f6f3ea
Author: Patrick East <email address hidden>
Date: Tue Aug 11 14:48:51 2015 -0700

    Switch Pure volume drivers to use Snapshot Objects

    Some consistency group operations require looking up snapshot objects
    and returning them. Now that we have Snapshot objects we should be using
    those.

    Change-Id: Ib4ff7fa3f7d768abb33e3b9436f7e64a3cd81f4c
    Closes-Bug: #1458126