certificate handler: fixup return code

Map a certificate install fail to a 400. This is likely due to an
invalid certificate.

Change-Id: Ie451aa356e4a708889aa7475f10a1c122253e859
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
diff --git a/module/obmc/wsgi/apps/rest_dbus.py b/module/obmc/wsgi/apps/rest_dbus.py
index 6066126..f52032a 100644
--- a/module/obmc/wsgi/apps/rest_dbus.py
+++ b/module/obmc/wsgi/apps/rest_dbus.py
@@ -922,7 +922,7 @@
             iface.Install(temp.name)
         except Exception as e:
             cleanup()
-            abort(503, str(e))
+            abort(400, str(e))
         cleanup()
 
     def do_delete(self):