client-side join chunks for GCS

Boto does not implement GCS's custom multipart API and so we're left to
join them client-side until it does.

storage/cloud.py

@@ -471,6 +471,15 @@ class GoogleCloudStorage(_CloudStorage):
 
     return key.size
 
+  def complete_chunked_upload(self, uuid, final_path, storage_metadata):
+    self._initialize_cloud_conn()
+
+    # Boto does not support GCS's multipart upload API because it differs from S3, so
+    # we are forced to join it all locally and then reupload.
+    # See https://github.com/boto/boto/issues/3355
+    chunk_list = self._chunk_list_from_metadata(storage_metadata)
+    self._client_side_chunk_join(final_path, chunk_list)
+
 
 class RadosGWStorage(_CloudStorage):
   def __init__(self, hostname, is_secure, storage_path, access_key, secret_key, bucket_name):