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_unit.py b/modules/libjuju/tests/integration/test_unit.py
index 1604c31..8b2251c 100644
--- a/modules/libjuju/tests/integration/test_unit.py
+++ b/modules/libjuju/tests/integration/test_unit.py
@@ -1,8 +1,8 @@
 import asyncio
-import pytest
-
 from tempfile import NamedTemporaryFile
 
+import pytest
+
 from .. import base
 
 
@@ -52,6 +52,11 @@
 @base.bootstrapped
 @pytest.mark.asyncio
 async def test_scp(event_loop):
+    # ensure that asyncio.subprocess will work;
+    try:
+        asyncio.get_child_watcher().attach_loop(event_loop)
+    except RuntimeError:
+        pytest.skip('test_scp will always fail outside of MainThread')
     async with base.CleanModel() as model:
         app = await model.deploy('ubuntu')