Sam-I-Am was reporting this in the nova IRC channel, same failure but with more details:

http://paste.openstack.org/show/488781/

In his case the host capabilities xml does not have a cpu model, so setting cpu_mode=none in nova.conf doesn't help, the details are in the stack trace:

2016-03-01 16:02:55.830 22615 ERROR oslo_service.service [req-5b0007bc-76b1-4ce1-86bb-2a79f73db1e7 - - - - -] Error starting thread.
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service Traceback (most recent call last):
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/oslo_service/service.py", line 680, in run_service
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     service.start()
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/nova/service.py", line 183, in start
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     self.manager.init_host()
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/nova/compute/manager.py", line 1309, in init_host
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     self.driver.init_host(host=self.host)
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 643, in init_host
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     self._do_quality_warnings()
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 621, in _do_quality_warnings
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     caps = self._host.get_capabilities()
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/nova/virt/libvirt/host.py", line 787, in get_capabilities
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     libvirt.VIR_CONNECT_BASELINE_CPU_EXPAND_FEATURES)
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/eventlet/tpool.py", line 186, in doit
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     result = proxy_call(self._autowrap, f, *args, **kwargs)
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/eventlet/tpool.py", line 144, in proxy_call
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     rv = execute(f, *args, **kwargs)
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/eventlet/tpool.py", line 125, in execute
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     six.reraise(c, e, tb)
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/eventlet/tpool.py", line 83, in tworker
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     rv = meth(*args, **kwargs)
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service   File "/opt/bbc/openstack-11.0-master/nova/local/lib/python2.7/site-packages/libvirt.py", line 3153, in baselineCPU
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service     if ret is None: raise libvirtError ('virConnectBaselineCPU() failed', conn=self)
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service libvirtError: XML error: Missing CPU model name
2016-03-01 16:02:55.830 22615 ERROR oslo_service.service

danpb said this about the failure:

danpb	Sam-I-Am: oh that's totally bogus and unrelated to the cpu_mode/cpu_model config options	16:05
danpb	Sam-I-Am: in the host.py  get_capabilities() method before it does                           [self._caps.host.cpu.to_xml()],	16:05
danpb	Sam-I-Am: it should check whether self._cps.host.cpu has a non-None model	16:06
danpb	Sam-I-Am: if the model is None, it should skip the baselineCPU() api call