openstack M版创建云主机No valid host was found. There are not

#创建云主机孵化的时候报错
查看对应计算节点nova的错误日志
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager [req-bc116e07-5e31-4d1d-be97-f09dd12e6aa3 2bda69e9096d4c4baee152f5cf430557 486299aff2314ec0b93ee0b49ea5bfd3 - - -] Instance failed network setup after 1 attempt(s)
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager Traceback (most recent call last):
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 1570, in _allocate_network_async
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager     bind_host_id=bind_host_id)
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager   File "/usr/lib/python2.7/site-packages/nova/network/neutronv2/api.py", line 668, in allocate_for_instance
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager     self._delete_ports(neutron, instance, created_port_ids)
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager   File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 220, in __exit__
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager     self.force_reraise()
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager   File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 196, in force_reraise
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager     six.reraise(self.type_, self.value, self.tb)
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager   File "/usr/lib/python2.7/site-packages/nova/network/neutronv2/api.py", line 657, in allocate_for_instance
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager     security_group_ids, available_macs, dhcp_opts)
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager   File "/usr/lib/python2.7/site-packages/nova/network/neutronv2/api.py", line 259, in _create_port
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager     raise exception.PortBindingFailed(port_id=port_id)
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager PortBindingFailed: Binding failed for port 7d238314-c5c5-434e-bc84-b513300132cc, please check neutron logs for more information.
2016-10-23 22:27:50.213 6624 ERROR nova.compute.manager
2016-10-23 22:27:50.214 6624 ERROR nova.compute.manager [req-bc116e07-5e31-4d1d-be97-f09dd12e6aa3 2bda69e9096d4c4baee152f5cf430557 486299aff2314ec0b93ee0b49ea5bfd3 - - -] [instance: 46b4ccdb-2d38-4e04-8b37-3da05e78b79c] Instance failed to spawn

解决方法：
计算节点
cat /etc/neutron/plugins/ml2/openvswitch_agent.ini
[ovs]
bridge_mappings = vlan:br-vlan