exception is not handled in the exception.

added an exception handler to handle the exception in the exception.

Change-Id: I05f911b37ec67318cb427ee145d2c4effec6f905
Closes-bug: #1550764

src/discovery/disc_auth_keystone.py

@@ -8,7 +8,10 @@
 try:
     from keystoneclient.middleware import auth_token
 except ImportError:
-    from keystonemiddleware import auth_token
+    try:
+        from keystonemiddleware import auth_token
+    except Exception:
+        pass
 except Exception:
     pass