Add an example post-deploy test:

- add a hoook to run all scripts under test/tests.d

- add an example test which verifies glance is up and contains
  the cirros image.

- configure root ssh key, so that tests over ssh don't need to
  use sudo everywhere.
- add an /etc/hosts entry to each vm to avoid extraneous 'unknown
  hosts' output.
- use ssh loglevel=none to avoid 'permananently added key' output