Wait for cloud-init to finish before provisioning

Before provisioning a native charm, a script is executed to wait until
cloud-init finishes. This will avoid some racing conditions.

Fixes bug 1184

Change-Id: Icc87f90f5941cf7b13bdd7dd01e5544122fb769e
Signed-off-by: David Garcia <david.garcia@canonical.com>
(cherry picked from commit 9074b05b)