Cleanup the config file on ./clean.sh

When users unstack and clean on devstack, the old config files
should be removed to avoid potential issues. As a result, users
will get a fresh new install on the next ./stack.sh

Change-Id: Ifd89dd7528d63a5e92dc9f02e939810c8fa2a247

devstack/plugin.sh

@@ -159,6 +159,10 @@ if is_service_enabled kuryr-libnetwork; then
             stop_process kuryr-libnetwork
         fi
     fi
+
+    if [[ "$1" == "clean" ]]; then
+        sudo rm -rf $KURYR_CONFIG_DIR
+    fi
 fi
 
 # Restore xtrace