some tempest fail when NEUTRON_CREATE_INITIAL_NETWORKS=True

some tempest fail when NEUTRON_CREATE_INITIAL_NETWORKS=True:

for example, tempest.scenario.test_network_basic_ops.TestNetworkBasicOps.test_mtu_sized_frames will fails.

initial root cause: cannot ssh to vm due (still need deep analysis)

workaround:

1. for all-in-one: remove all public/private network and recreate public network as:

source $DEVSTACK_PATH/openrc admin
openstack router unset --external-gateway router1
openstack port list --router router1 -c ID -f value | xargs -I {} openstack router remove port router1 {}
openstack router delete router1
openstack subnet list | grep -e public -e private | cut -f2 -d'|' | xargs openstack subnet delete
openstack network list | grep -e public -e private | cut -f2 -d'|' | xargs openstack network delete
openstack network create public --external --provider-network-type=flat --provider-physical-network=public
openstack subnet create --network=public --subnet-range=172.24.5.0/24 --gateway 172.24.5.1 public-subnet

2. for multi-node: create public network after all compute nodes are up