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/devserver.py b/devserver.py
index fcd73fb..80cd977 100755
--- a/devserver.py
+++ b/devserver.py
@@ -285,6 +285,7 @@
       except:
         # On any exception, reset the state of the downloader_dict.
         self._downloader_dict[archive_url] = None
+        raise
 
   @cherrypy.expose
   def wait_for_status(self, **kwargs):