libvirtd problem - error from service: ListActivatableNames: Connection is closed

Issue

• After rebooting all hosts, VMs cannot launched anymore. They stay in error state. From nova compute logs:

2015-09-22 08:48:47.690 5418 ERROR nova.compute.manager [-] [instance: 5ea265ec-848a-410a-8510-8e924cdedb80] Instance failed to spawn
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80] Traceback (most recent call last):
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2288, in _build_resources
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     yield resources
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2158, in _build_and_run_instance
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     block_device_info=block_device_info)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 2635, in spawn
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     block_device_info, disk_info=disk_info)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 4558, in _create_domain_and_network
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     power_on=power_on)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 4482, in _create_domain
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     LOG.error(err)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/nova/openstack/common/excutils.py", line 82, in __exit__
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     six.reraise(self.type_, self.value, self.tb)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 4472, in _create_domain
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     domain.createWithFlags(launch_flags)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 183, in doit
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     result = proxy_call(self._autowrap, f, *args, **kwargs)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 141, in proxy_call
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     rv = execute(f, *args, **kwargs)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 122, in execute
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     six.reraise(c, e, tb)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 80, in tworker
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     rv = meth(*args, **kwargs)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]   File "/usr/lib64/python2.7/site-packages/libvirt.py", line 996, in createWithFlags
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80]     if ret == -1: raise libvirtError ('virDomainCreateWithFlags() failed', dom=self)
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80] libvirtError: error from service: ListActivatableNames: Connection is closed
2015-09-22 08:48:47.690 5418 TRACE nova.compute.manager [instance: 5ea265ec-848a-410a-8510-8e924cdedb80] 
2015-09-22 08:48:47.691 5418 AUDIT nova.compute.manager [req-01c93cc2-9ab1-4a9f-b018-efbedf996b17 None] [instance: 5ea265ec-848a-410a-8510-8e924cdedb80] Terminating instance
2015-09-22 08:48:47.701 5418 INFO nova.virt.libvirt.driver [-] [instance: 5ea265ec-848a-410a-8510-8e924cdedb80] Instance destroyed successfully.