image load: don't depend on deprecated JSONMessage.error field

The error field  was deprecated in favor of the errorDetail struct in
[moby@3043c26], but the API continued to return both. This patch updates
docker-py to not depend on the deprecated field.

[moby@3043c26]: moby/moby@3043c26

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docker/models/images.py

@@ -407,8 +407,8 @@ def load(self, data):
                 if match:
                     image_id = match.group(2)
                     images.append(image_id)
-            if 'error' in chunk:
-                raise ImageLoadError(chunk['error'])
+            if 'errorDetail' in chunk:
+                raise ImageLoadError(chunk['errorDetail']['message'])
 
         return [self.get(i) for i in images]