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/livemodel.py b/modules/libjuju/examples/livemodel.py
index a15e9f7..1b10ac9 100644
--- a/modules/libjuju/examples/livemodel.py
+++ b/modules/libjuju/examples/livemodel.py
@@ -6,8 +6,6 @@
 3. Runs forever (kill with Ctrl-C)
 
 """
-import asyncio
-
 from juju.model import Model
 from juju import loop
 
@@ -21,6 +19,7 @@
 
 async def watch_model():
     model = Model()
+    # connect to current model with current user, per Juju CLI
     await model.connect()
 
     model.add_observer(on_model_change)