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/overrides.py b/modules/libjuju/juju/client/overrides.py
index 5e98e56..8b29de7 100644
--- a/modules/libjuju/juju/client/overrides.py
+++ b/modules/libjuju/juju/client/overrides.py
@@ -1,10 +1,8 @@
-from collections import namedtuple
 import re
+from collections import namedtuple
 
+from . import _client, _definitions
 from .facade import ReturnMapping, Type, TypeEncoder
-from .import _client
-from .import _definitions
-
 
 __all__ = [
     'Delta',