replace left quantum string for enable_lb

writing the correct config for horizon to show LBaaS entry properly
like:

OPENSTACK_NEUTRON_NETWORK = {
    'enable_lb': True
}

Change-Id: I7f522a150a3732ee734f2b818910ff92c8c73028
Fixes: bug #1200098
diff --git a/lib/horizon b/lib/horizon
index 0cc250e..b537484 100644
--- a/lib/horizon
+++ b/lib/horizon
@@ -106,7 +106,7 @@
 
     # enable loadbalancer dashboard in case service is enabled
     if is_service_enabled q-lbaas; then
-        _horizon_config_set $local_settings OPENSTACK_QUANTUM_NETWORK enable_lb True
+        _horizon_config_set $local_settings OPENSTACK_NEUTRON_NETWORK enable_lb True
     fi
 
     # Initialize the horizon database (it stores sessions and notices shown to