New N2VC interface + updated libjuju

This commit introduces the Python3 N2VC module, which acts as a standard
interface to the VCA.

The goal of this is to provide a common way for modules to interface
with the VCA.

- Updated libjuju from 0.6.1 to 0.7.3

Signed-off-by: Adam Israel <adam.israel@canonical.com>
Change-Id: Ide70fb5ae5797eb6486de24653dc09a23f9c009e
diff --git a/modules/libjuju/tests/integration/test_client.py b/modules/libjuju/tests/integration/test_client.py
index e4c9c92..240c471 100644
--- a/modules/libjuju/tests/integration/test_client.py
+++ b/modules/libjuju/tests/integration/test_client.py
@@ -1,7 +1,7 @@
-import pytest
-
 from juju.client import client
 
+import pytest
+
 from .. import base
 
 
@@ -9,7 +9,7 @@
 @pytest.mark.asyncio
 async def test_user_info(event_loop):
     async with base.CleanModel() as model:
-        controller_conn = await model.connection.controller()
+        controller_conn = await model.connection().controller()
 
         um = client.UserManagerFacade.from_connection(controller_conn)
         result = await um.UserInfo(