virt: convert hardware module to use nova.objects.ImageMeta

Convert the APIs in the nova.virt.hardware module to expect to
receive an instance of nova.objects.ImageMeta instead of a
dict.

Update the virt drivers to convert the dict into an ImageMeta
module, as a stepping stone, until they to are converted to
use ImageMeta throughout.

Change-Id: Iac034d864cd0265759aaa7c8049fafa276763cc0

nova/tests/unit/image/fake.py

@@ -79,8 +79,8 @@ class _FakeImageService(object):
                  'deleted': False,
                  'status': 'active',
                  'is_public': True,
-                 'container_format': None,
-                 'disk_format': None,
+                 'container_format': 'bare',
+                 'disk_format': 'raw',
                  'size': '83594576',
                  'properties': {'kernel_id': CONF.null_kernel,
                                 'ramdisk_id': CONF.null_kernel}}