only remove network states from Nova when n-net is enabled

When n-net is not enabled but q-dhcp is enabled then it's not
necessary to remove the states directory of nova-network.

Change-Id: Ib4b37aa7df2b3cda3048b278ddad24e87e3744c9
diff --git a/stack.sh b/stack.sh
index c715a85..4de79bb 100755
--- a/stack.sh
+++ b/stack.sh
@@ -1001,9 +1001,13 @@
     fi
 
     clean_iptables
-    rm -rf ${NOVA_STATE_PATH}/networks
-    sudo mkdir -p ${NOVA_STATE_PATH}/networks
-    safe_chown -R ${USER} ${NOVA_STATE_PATH}/networks
+
+    if is_service_enabled n-net; then
+        rm -rf ${NOVA_STATE_PATH}/networks
+        sudo mkdir -p ${NOVA_STATE_PATH}/networks
+        safe_chown -R ${USER} ${NOVA_STATE_PATH}/networks
+    fi
+
     # Force IP forwarding on, just in case
     sudo sysctl -w net.ipv4.ip_forward=1
 fi