Fix bug where we don't re-raise an exception in download.

This bug was introduced such that we could return 200 without
'Success'.

I also renamed the devserver unittests to be consistent with the others.

BUG=chromium-os:32072
TEST=devserver_unittest.py

Change-Id: Ibe1c4e1c8506ea919430297e018de98c6b824fb2
Reviewed-on: https://gerrit.chromium.org/gerrit/26497
Tested-by: Chris Sosa <sosa@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
Commit-Ready: Chris Sosa <sosa@chromium.org>
diff --git a/downloader.py b/downloader.py
index beb57c2..7f53ec3 100755
--- a/downloader.py
+++ b/downloader.py
@@ -255,6 +255,7 @@
       raise
     finally:
       self._Cleanup()
+
     return 'Success'
 
   def GatherArtifactDownloads(self, temp_download_dir, archive_url, short_build,