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/frontend/afe/site_rpc_interface.py b/frontend/afe/site_rpc_interface.py
index f82731b..818f3d1 100644
--- a/frontend/afe/site_rpc_interface.py
+++ b/frontend/afe/site_rpc_interface.py
@@ -71,10 +71,8 @@
     ds = dev_server.DevServer.create()
     timings['download_started_time'] = datetime.datetime.now().strftime(
         time_fmt)
-    try:
-        ds.trigger_download(build, synchronous=False)
-    except dev_server.DevServerException as e:
-        raise error.StageBuildFailure(e)
+    if not ds.trigger_download(build, synchronous=False):
+        raise error.StageBuildFailure("Server error while staging " + build)
     timings['payload_finished_time'] = datetime.datetime.now().strftime(
         time_fmt)