Fix a couple of charm test issues.
Fix a couple of charm test issues.

Add test for case of charm with no config and destroy the container at the end
of each test.

R=hazmat
CC=
https://codereview.appspot.com/6580044

mitechie/juju-gui,bac/juju-gui,jrwren/juju-gui,mitechie/juju-gui,bac/juju-gui,jrwren/juju-gui,mitechie/juju-gui,bac/juju-gui,jrwren/juju-gui,bac/juju-gui,CanonicalJS/juju-gui,CanonicalJS/juju-gui,mitechie/juju-gui,CanonicalJS/juju-gui,jrwren/juju-gui