Revert "reduce default lease time to 5 minutes"

We have a fix in Nova which should make this unessessary,
revert to see if that's true.

This reverts commit 61aa0e9.

Change-Id: If109af452ad583417e3a3a3ef1c9b545f1ec9b89

Author: sdague

lib/nova

@@ -689,8 +689,6 @@ function create_nova_conf_nova_network {
     iniset $NOVA_CONF DEFAULT public_interface "$PUBLIC_INTERFACE"
     iniset $NOVA_CONF DEFAULT vlan_interface "$VLAN_INTERFACE"
     iniset $NOVA_CONF DEFAULT flat_network_bridge "$FLAT_NETWORK_BRIDGE"
-    # force down dhcp leases to 5 minutes, which lets us expire faster
-    iniset $NOVA_CONF DEFAULT dhcp_lease_time 300
     if [ -n "$FLAT_INTERFACE" ]; then
         iniset $NOVA_CONF DEFAULT flat_interface "$FLAT_INTERFACE"
     fi