Improved Primitive support and better testing

This changeset addresses several issues.

- Improve primitive support so the status and output of an executed
primitive can be retrieved
- Merge latest upstream libjuju (required for new primive features)
- New testing framework
    This is the start of a new testing framework with the ability to
create and configure LXD containers with SSH, to use while testing proxy
charms.
- Add support for using ssh keys with proxy charms
    See Feature 1429. This uses the per-proxy charm/unit ssh keypair

Signed-off-by: Adam Israel <adam.israel@canonical.com>
diff --git a/modules/libjuju/examples/controller.py b/modules/libjuju/examples/controller.py
index 3f029ab..b61a6f6 100644
--- a/modules/libjuju/examples/controller.py
+++ b/modules/libjuju/examples/controller.py
@@ -8,7 +8,6 @@
 5. Destroys the model
 
 """
-import asyncio
 import logging
 
 from juju.controller import Controller
@@ -17,6 +16,7 @@
 
 async def main():
     controller = Controller()
+    # connect to current controller with current user, per Juju CLI
     await controller.connect()
     model = await controller.add_model(
         'my-test-model',