Better error handling, itterate on json stream directly.

Signed-off-by: Aaron Cowdin <aaron.cowdin@gmail.com>

docker/models/images.py

@@ -166,19 +166,18 @@ class ImageCollection(Collection):
         resp = self.client.api.build(**kwargs)
         if isinstance(resp, six.string_types):
             return self.get(resp)
-        events = list(json_stream(resp))
-        if not events:
-            return BuildError('Unknown')
-        for event in events:
-            if 'stream' in event:
+        for chunk in json_stream(resp):
+            if 'error' in chunk:
+                raise BuildError(chunk['error'])
+                break
+            if 'stream' in chunk:
                 match = re.search(r'(Successfully built |sha256:)([0-9a-f]+)',
-                                  event.get('stream', ''))
+                                  chunk['stream'])
                 if match:
                     image_id = match.group(2)
                     return self.get(image_id)
 
-        event = events[-1]
-        raise BuildError(event.get('error') or event)
+        return BuildError('Unknown')
 
     def get(self, name):
         """