Correct the error type in the report for goldfish AVD type.

Bug: 178436311
Test: acloud-dev create_gf --build_target sdk_gphone_x86_64-userdebug \
      --branch git_master --build_id P19033239 --report-file report.json
Change-Id: I88198db2fad707aebf9d7a7b865c3ff5415aa856
diff --git a/errors.py b/errors.py
index fc6a084..5b6d249 100644
--- a/errors.py
+++ b/errors.py
@@ -41,7 +41,7 @@
 
     def __init__(self, code, message):
         self.code = code
-        super(HttpError, self).__init__(message)
+        super().__init__(message)
 
     @staticmethod
     def CreateFromHttpError(http_error):
@@ -83,6 +83,10 @@
     """To catch device boot errors."""
 
 
+class DownloadArtifactError(DriverError):
+    """To catch download artifact errors."""
+
+
 class NoSubnetwork(DriverError):
     """When there is no subnetwork for the GCE."""