Don't require lp:landscape-charm to be in ~

There still isn't a totally unsupervised way to do the landscape install since
they require the private/unreleased PPA. Users need to follow the instructions
at /usr/share/cloud-install/templates/landscape-deployments.yaml (which include
canonical-only accessible parts at this point).
Merge pull request #91 from Ubuntu-Solutions-Engineering/landscape-refactoring

Don't require lp:landscape-charm to be in ~