Tacker fails to register openstack VIM

I am using Tacker (master commit 46a28fc8) with devstack to connect external openstack.

I register VIM with config:
auth_url: 'http://keystone.ocloud.test/v3' # I also tried 'http://keystone.ocloud.test'
username: 'admin'
password: 'xxxxxx'
project_name: 'admin'
project_domain_name: 'Default'
user_domain_name: 'Default'
#cert_verify: 'False'

Run command "openstack vim register --config-file ./vim_config_openstack.yaml vim-openstack" response internal error.

I trace tacker source code, and find cause.

In tacker/tacker/nfvo/drivers/vim/openstack_driver.py:
OpenStack_Driver::register_vim
   self.discover_placement_attr(vim_obj, ks_client)
     regions = self._find_regions(ks_client)
       resp = ks_client.get('/v3/regions')

_find_regions calls ks_client.get with '/v3/regions'.
However, I capture the http packet and find that the real request URL sent to VIM is '/v3/v3/regions'.

After moidfy the code to ks_client.get('/regions'), openstack VIM can register success.

I am not sure this is tacker's BUG, keystoneauth1's BUG or I misconfig something.