Revert "[autotest] Put dev server error strings in exceptions"

This change exposed a bug in the old test_scheduler. The old test_scheduler
didn't do anything to suppress exceptions and aborts if the devserver returns
any exceptions.

This change is good as is and can be safely re-reverted once the old test_scheduler is robustified a little.

This reverts commit c807fcb56c57dbac1b193d92a90d59388c0cefe4

BUG=chromium-os:30915
TEST=Ran on autotest server with test_scheduler.

Change-Id: I22b9bbf87552c411c82b2d4e67fdbc33576eacb6
Reviewed-on: https://gerrit.chromium.org/gerrit/22776
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
diff --git a/server/cros/control_file_getter.py b/server/cros/control_file_getter.py
index 4393c6b..2f83538 100644
--- a/server/cros/control_file_getter.py
+++ b/server/cros/control_file_getter.py
@@ -193,12 +193,12 @@
         |self._dev_server|.  Populates |self._files| with that list
         and then returns paths (under the autotest dir) to them.
 
-        @return A list of control file paths.
+        @return A list of control file paths.  None on failure.
         @throws NoControlFileList if there is an error while listing.
         """
         try:
             return self._dev_server.list_control_files(self._build)
-        except dev_server.DevServerException as e:
+        except urllib2.HTTPError as e:
             raise error.NoControlFileList(e)
 
 
@@ -214,5 +214,5 @@
         """
         try:
             return self._dev_server.get_control_file(self._build, test_path)
-        except dev_server.DevServerException as e:
+        except urllib2.HTTPError as e:
             raise error.ControlFileNotFound(e)