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/juju/client/_definitions.py b/modules/libjuju/juju/client/_definitions.py
index 198784d..fde035f 100644
--- a/modules/libjuju/juju/client/_definitions.py
+++ b/modules/libjuju/juju/client/_definitions.py
@@ -1,7 +1,7 @@
 # DO NOT CHANGE THIS FILE! This file is auto-generated by facade.py.
 # Changes will be overwritten/lost when the file is regenerated.
 
-from juju.client.facade import Type, ReturnMapping
+from juju.client.facade import ReturnMapping, Type
 
 
 class APIHostPortsResult(Type):
@@ -8018,5 +8018,3 @@
         results : typing.Sequence<+T_co>[~ZoneResult]<~ZoneResult>
         '''
         self.results = [ZoneResult.from_json(o) for o in results or []]
-
-