fuel2 plugins sync command failed without plugins

Env description:
[root@nailgun ~]# fuel2 fuel-version
+-------------------+-------------+
| Field | Value |
+-------------------+-------------+
| api | 1 |
| auth_required | True |
| feature_groups | [] |
| openstack_version | newton-10.0 |
| release | 10.0 |
+-------------------+-------------+

[root@nailgun ~]# cat /etc/fuel_build_id
1542
[root@nailgun ~]# cat /etc/fuel_build_number
1542
[root@nailgun ~]# cat /etc/fuel_release
10.0

steps to reproduce:
  1. deploy 10.0 env
  2. run command "fuel2 plugins sync"
  3. notice - there is no installed plugins

expected result:
  command returned simple warning message

result:
[root@nailgun ~]# fuel2 plugins sync │------------- ------------------- ----------------------------------------------------------------------
500 Server Error: Internal Server Error for url: http://10.109.0.2:8000/api/v1/plugins/sync/ (Traceback (m│-------------------------
ost recent call last): │empty 2017-03-30 08:50:46 admin, slave-01, slave-02, slave-03, slave-04, slave-05, slave-06, sla
  File "/usr/lib/python2.7/site-packages/nailgun/api/v1/handlers/base.py", line 308, in handle_errors │ve-07, slave-08, slave-09
    return func(cls, *args, **kwargs) │ready 2017-03-30 08:54:20 admin, slave-01, slave-02, slave-03, slave-04, slave-05, slave-06, sla
  File "<string>", line 2, in POST │ve-07, slave-08, slave-09
  File "/usr/lib/python2.7/site-packages/nailgun/api/v1/handlers/base.py", line 366, in validate │ceph_rados_gw 2017-03-30 10:26:26 admin, slave-01, slave-02, slave-03, slave-04, slave-05, slave-06, sla
    return func(cls, *args, **kwargs) │ve-07, slave-08, slave-09
  File "/usr/lib/python2.7/site-packages/nailgun/api/v1/handlers/plugin.py", line 77, in POST │(100-venv)vnaumov@tpi77:~$ lab snapshot-delete 10.0.fuel.1542 empty
    PluginManager.sync_plugins_metadata(plugin_ids=ids) │(100-venv)vnaumov@tpi77:~$ lab snapshot-delete 10.0.fuel.1542 ready
  File "/usr/lib/python2.7/site-packages/nailgun/plugins/manager.py", line 630, in sync_plugins_metadata │(100-venv)vnaumov@tpi77:~$
    cls._install_or_update_or_delete_plugins() │
  File "/usr/lib/python2.7/site-packages/nailgun/plugins/manager.py", line 646, in _install_or_update_or_d│
elete_plugins │
    for plugin_dir in cls._list_plugins_on_fs(): │
  File "/usr/lib/python2.7/site-packages/nailgun/plugins/manager.py", line 725, in _list_plugins_on_fs │
    return os.listdir(settings.PLUGINS_PATH) │
OSError: [Errno 2] No such file or directory: '/var/www/nailgun/plugins' │
)