Nova-docker on liberty start error

2016-09-07 16:02:35.903 7362 INFO nova.virt.driver [-] Loading compute driver 'novadocker.virt.docker.DockerDriver'
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver [-] Unable to load the virtualization driver
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver Traceback (most recent call last):
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver   File "/usr/lib/python2.7/site-packages/nova/virt/driver.py", line 1454, in load_compute_driver
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver     virtapi)
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver   File "/usr/lib/python2.7/site-packages/oslo_utils/importutils.py", line 52, in import_object_ns
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver     return import_class(import_str)(*args, **kwargs)
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver   File "/usr/lib/python2.7/site-packages/oslo_utils/importutils.py", line 27, in import_class
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver     __import__(mod_str)
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver   File "/usr/lib/python2.7/site-packages/novadocker/virt/docker/__init__.py", line 20, in <module>
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver     from novadocker.virt.docker import driver
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver   File "/usr/lib/python2.7/site-packages/novadocker/virt/docker/driver.py", line 27, in <module>
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver     from docker import errors
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver ImportError: No module named docker
2016-09-07 16:02:35.905 7362 ERROR nova.virt.driver