some ERROR log entries when create external network

Some ERROR/WARN entries observed when successfully creating external network and setting router gateway. We need to verify if these ERROR/WARN are valid or not.

Steps:

1) Stack fresh openstack and ODL
2) Create external network/subnet:

neutron net-create ext-net --router:external --provider:physical_network public --provider:network_type flat

neutron subnet-create --name ext-subnet --allocation-pool start=192.168.56.9,end=192.168.56.14 --disable-dhcp --gateway 192.168.56.1 ext-net 192.168.56.0/24

3) Add router and set Gateway
neutron router-create ext-rtr
neutron router-gateway-set ext-rtr ext-net

4) clear Router GW

neutron router-gateway-clear ext-rtr

5) Except for the Exception as result of step 4) (NETVIRT-838), steps 1 to 3 seem to work fine. However there are some ERROR/WARN in the karaf log.