Fix handling of four byte utf8 manifests

- Adds the charset: utf-8 to all the manifest responses
- Makes sure we connect to MySQL in utf8mb4 mode, to ensure we can properly read and write 4-byte utf8 strings
- Adds tests for all of the above

test/registry/protocol_fixtures.py

@@ -138,6 +138,20 @@ def images_with_empty_layer():
   ]
 
 
+@pytest.fixture(scope="session")
+def unicode_emoji_images():
+  """ Returns basic images for push and pull testing that contain unicode in the image metadata. """
+  # Note: order is from base layer down to leaf.
+  parent_bytes = layer_bytes_for_contents('parent contents')
+  image_bytes = layer_bytes_for_contents('some contents')
+  return [
+    Image(id='parentid', bytes=parent_bytes, parent_id=None),
+    Image(id='someid', bytes=image_bytes, parent_id='parentid',
+          config={'comment': u'😱',
+                  'author': u'Sômé guy'}),
+  ]
+
+
 @pytest.fixture(scope="session")
 def jwk():
   return RSAKey(key=RSA.generate(2048))