Fix bug 680

This patch adds two new methods, Subscribe and Unsubscribe, allowing the
caller to subscribe to callback messages for an already deployed charm.

Change-Id: I1e34b488914feb488cf80b157fd664ca37037e76
Signed-off-by: Adam Israel <adam.israel@canonical.com>
diff --git a/Makefile b/Makefile
index abc2c39..fab6991 100644
--- a/Makefile
+++ b/Makefile
@@ -3,6 +3,7 @@
 	find . -name *.pyc -delete
 	rm -rf .tox
 	rm -rf tests/charms/builds/*
+	lxc list test- --format=json|jq '.[]["name"]'| xargs lxc delete --force
 .tox:
 	tox -r --notest
 test: lint