I guess network_allocate_retries won't help since that's not in the driver spawn code path that's failing:

2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [req-2b591b2c-36f0-494b-a5b2-06dc2a783c49 tempest-MultipleCreateTestJSON-64962745 tempest-MultipleCreateTestJSON-1348265215] [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d] Instance failed to spawn
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d] Traceback (most recent call last):
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/opt/stack/new/nova/nova/compute/manager.py", line 2193, in _build_resources
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     yield resources
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/opt/stack/new/nova/nova/compute/manager.py", line 2039, in _build_and_run_instance
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     block_device_info=block_device_info)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/opt/stack/new/nova/nova/virt/libvirt/driver.py", line 2767, in spawn
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     block_device_info=block_device_info)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/opt/stack/new/nova/nova/virt/libvirt/driver.py", line 4906, in _create_domain_and_network
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     xml, pause=pause, power_on=power_on)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/opt/stack/new/nova/nova/virt/libvirt/driver.py", line 4837, in _create_domain
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     guest.launch(pause=pause)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/opt/stack/new/nova/nova/virt/libvirt/guest.py", line 142, in launch
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     self._encoded_xml, errors='ignore')
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     self.force_reraise()
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     six.reraise(self.type_, self.value, self.tb)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/opt/stack/new/nova/nova/virt/libvirt/guest.py", line 137, in launch
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     return self._domain.createWithFlags(flags)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/usr/local/lib/python2.7/dist-packages/eventlet/tpool.py", line 186, in doit
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     result = proxy_call(self._autowrap, f, *args, **kwargs)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/usr/local/lib/python2.7/dist-packages/eventlet/tpool.py", line 144, in proxy_call
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     rv = execute(f, *args, **kwargs)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/usr/local/lib/python2.7/dist-packages/eventlet/tpool.py", line 125, in execute
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     six.reraise(c, e, tb)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/usr/local/lib/python2.7/dist-packages/eventlet/tpool.py", line 83, in tworker
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     rv = meth(*args, **kwargs)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]   File "/usr/local/lib/python2.7/dist-packages/libvirt.py", line 1059, in createWithFlags
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]     if ret == -1: raise libvirtError ('virDomainCreateWithFlags() failed', dom=self)
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d] libvirtError: internal error: libxenlight failed to create new domain 'instance-0000003c'
2016-03-04 07:17:13.370 8173 ERROR nova.compute.manager [instance: eb3ec27f-53c0-4ce7-a6ad-58f9bb37b25d]