_configure_neutron_dhcp_agent: Modify the right config file

This has been incorrect since the initial commit
(I632df4149e9d7f78cb5a7091dfe4ea8f8ca3ddfa)

Closes-Bug: #1483499
Change-Id: Ife4defce989c4f3c7eb5381376c0f93de50a9668
diff --git a/lib/neutron-legacy b/lib/neutron-legacy
index 4069439..6412609 100644
--- a/lib/neutron-legacy
+++ b/lib/neutron-legacy
@@ -979,7 +979,7 @@
     iniset $Q_DHCP_CONF_FILE DEFAULT use_namespaces $Q_USE_NAMESPACE
     iniset $Q_DHCP_CONF_FILE DEFAULT root_helper "$Q_RR_COMMAND"
     if [[ "$Q_USE_ROOTWRAP_DAEMON" == "True" ]]; then
-        iniset $NEUTRON_TEST_CONFIG_FILE agent root_helper_daemon "$Q_RR_DAEMON_COMMAND"
+        iniset $Q_DHCP_CONF_FILE agent root_helper_daemon "$Q_RR_DAEMON_COMMAND"
     fi
 
     if ! is_service_enabled q-l3; then