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/examples/controller.py b/modules/libjuju/examples/controller.py
index 6002f68..3f029ab 100644
--- a/modules/libjuju/examples/controller.py
+++ b/modules/libjuju/examples/controller.py
@@ -17,7 +17,7 @@
 
 async def main():
     controller = Controller()
-    await controller.connect_current()
+    await controller.connect()
     model = await controller.add_model(
         'my-test-model',
         'aws',