Update stack.sh to pass quantum.conf to DHCP agent

The DHCP agent now utiliizes the the main Quantum configuration file to
get RPC information.

Change-Id: Ia42350d7d18ff25a77712a43ff20bc4669174380
diff --git a/stack.sh b/stack.sh
index ccbbc6b..7c709cb 100755
--- a/stack.sh
+++ b/stack.sh
@@ -1234,7 +1234,7 @@
 screen_it q-agt "sudo python $AGENT_BINARY --config-file $Q_CONF_FILE --config-file /$Q_PLUGIN_CONF_FILE"
 
 # Start up the quantum agent
-screen_it q-dhcp "sudo python $AGENT_DHCP_BINARY --config-file=$Q_DHCP_CONF_FILE"
+screen_it q-dhcp "sudo python $AGENT_DHCP_BINARY --config-file $Q_CONF_FILE --config-file=$Q_DHCP_CONF_FILE"
 
 # Nova
 # ----