compat: image normalization: handle sha256 prefix

When normalizing image names on the compat API, make sure to take the
`sha256:` prefix into account when matching against the image ID.
Otherwise, the name will mistakingly be subject to docker.io
normalization.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>
Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

test/python/docker/compat/test_images.py

@@ -79,6 +79,7 @@ class TestImages(unittest.TestCase):
         # Add more images
         self.client.images.pull(constant.BB)
         self.assertEqual(len(self.client.images.list()), 2)
+        self.assertEqual(len(self.client.images.list(all=True)), 2)
 
         # List images with filter
         self.assertEqual(len(self.client.images.list(filters={"reference": "alpine"})), 1)