Native charm support

This patch adds a provisioner which will prepare a VM, via SSH, to run the Juju
agent, enabling a native charm to run on the VM.

Change-Id: Icd5d873a12e2d7b2e7cb5424e87d8083a7921c16
Signed-off-by: Adam Israel <adam.israel@canonical.com>
(cherry picked from commit 0cd1c02c)