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/errors.py b/modules/libjuju/juju/errors.py
index ecd1c0d..da11cdb 100644
--- a/modules/libjuju/juju/errors.py
+++ b/modules/libjuju/juju/errors.py
@@ -25,3 +25,25 @@
 
 class JujuConnectionError(ConnectionError, JujuError):
     pass
+
+
+class JujuAuthError(JujuConnectionError):
+    pass
+
+
+class JujuRedirectException(Exception):
+    """Exception indicating that a redirection was requested"""
+    def __init__(self, redirect_info):
+        self.redirect_info = redirect_info
+
+    @property
+    def ca_cert(self):
+        return self.redirect_info['ca-cert']
+
+    @property
+    def endpoints(self):
+        return [
+            ('{value}:{port}'.format(**s), self.ca_cert)
+            for servers in self.redirect_info['servers']
+            for s in servers if s['scope'] == 'public'
+        ]