manage.py dropdb/syncdb/loaddefault don't work

I cloned the latest fuel codes from git and made iso. Then fuel server is installed successfully. When I created some environments, just tried to clean all of them with /usr/bin/manage.py dropdb but failed.

Traceback (most recent call last):
  File "./var/lib/docker/devicemapper/mnt/5acb848c8df3a7051a0708980fa1286e09c925f0b4f8e017973d66bae94aacbb/rootfs/usr/bin/manage.py", line 302, in <module>
    action(params) if action else parser.print_help()
  File "./var/lib/docker/devicemapper/mnt/5acb848c8df3a7051a0708980fa1286e09c925f0b4f8e017973d66bae94aacbb/rootfs/usr/bin/manage.py", line 195, in action_dropdb
    from nailgun.db import dropdb
ImportError: No module named nailgun.db

Not familiar with the way of fuel version 5.1 to 6.0 to reset the server, just need a hand. Appreciate.