devserver: fix a bug with __init__ keyword arguments

BUG=None
TEST=downloader_unittest.py passes.

Change-Id: I7bf650b0460e00f6c981781328dd90c65a6ee325
Reviewed-on: https://chromium-review.googlesource.com/176908
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
diff --git a/build_artifact.py b/build_artifact.py
index d1623b6..bb8ec46 100755
--- a/build_artifact.py
+++ b/build_artifact.py
@@ -438,8 +438,8 @@
 class AutotestTarballBuildArtifact(TarballBuildArtifact):
   """Wrapper around the autotest tarball to download from gsutil."""
 
-  def __init__(self, *args):
-    super(AutotestTarballBuildArtifact, self).__init__(*args)
+  def __init__(self, *args, **dargs):
+    super(AutotestTarballBuildArtifact, self).__init__(*args, **dargs)
     # We don't store/check explicit file lists in Autotest tarball markers;
     # this can get huge and unwieldy, and generally make little sense.
     self.store_installed_files = False