docker daemon关闭后novadocker的报错

[gukai]

应该捕获错误并处理，避免如下报错
nager._sync_power_states: ('Connection aborted.', error(111, 'ECONNREFUSED'))
Traceback (most recent call last):
File "/usr/lib/python2.6/site-packages/nova/openstack/common/periodic_task.py", line 198, in run_periodic_tasks
task(self, context)
File "/usr/lib/python2.6/site-packages/nova/compute/manager.py", line 5746, in _sync_power_states
num_vm_instances = self.driver.get_num_instances()
File "/usr/lib/python2.6/site-packages/nova/virt/driver.py", line 187, in get_num_instances
return len(self.list_instances())
File "/usr/lib/python2.6/site-packages/novadocker/virt/docker/driver.py", line 126, in list_instances
for container in self.docker.containers(all=True):
File "/usr/lib/python2.6/site-packages/novadocker/virt/docker/client.py", line 34, in wrapper
out = f(_args, *_kwds)
File "/usr/lib/python2.6/site-packages/docker/api/container.py", line 68, in containers
res = self._result(self._get(u, params=params), True)
File "/usr/lib/python2.6/site-packages/docker/client.py", line 110, in _get
return self.get(url, *_self._set_request_timeout(kwargs))
File "/usr/lib/python2.6/site-packages/novadocker/virt/docker/client.py", line 34, in wrapper
out = f(_args, *_kwds)
File "/usr/lib/python2.6/site-packages/requests/sessions.py", line 480, in get
return self.request('GET', url, *_kwargs)
File "/usr/lib/python2.6/site-packages/novadocker/virt/docker/client.py", line 34, in wrapper
out = f(_args, *_kwds)
File "/usr/lib/python2.6/site-packages/requests/sessions.py", line 468, in request
resp = self.send(prep, *_send_kwargs)
File "/usr/lib/python2.6/site-packages/novadocker/virt/docker/client.py", line 34, in wrapper
out = f(_args, *_kwds)
File "/usr/lib/python2.6/site-packages/requests/sessions.py", line 576, in send
r = adapter.send(request, *_kwargs)
File "/usr/lib/python2.6/site-packages/requests/adapters.py", line 412, in send
raise ConnectionError(err, request=request)
ConnectionError: ('Connection aborted.', error(111, 'ECONNREFUSED'))