Snapshot and volume objects

Abstract volumes and volume snapshots into objects.
Get, create, and delete snapshot APIs were changed to
use new snapshot objects.  A skeleton volume object was
created, but cinder internals were not changed to use
the volume object, although volume is referenced and
used by the snapshot object.  The internals will be
changed to use volume object in a subsequent patch.

Change-Id: I387018e80c8539565e99454db65d976030002c0f
Implements: blueprint cinder-objects

cinder/test.py

@@ -42,6 +42,7 @@ from cinder.common import config  # noqa Need to register global_opts
 from cinder.db import migration
 from cinder.db.sqlalchemy import api as sqla_api
 from cinder import i18n
+from cinder import objects
 from cinder.openstack.common import log as oslo_logging
 from cinder import rpc
 from cinder import service
@@ -106,6 +107,9 @@ class TestCase(testtools.TestCase):
         """Run before each test method to initialize test environment."""
         super(TestCase, self).setUp()
 
+        # Import cinder objects for test cases
+        objects.register_all()
+
         # Unit tests do not need to use lazy gettext
         i18n.enable_lazy(False)