Comment 1 for bug 1135335

From reading the docs at https://juju.ubuntu.com/docs/provider-configuration-openstack.html we will need to support the following env variables (everything supports being defined in environment.yaml):

 * "access_key": NOVA_API_KEY env variable
 * "secret_key": EC2_SECRET_KEYS env variable (or AWS_SECRET_ACCESS_KEY, judging by code of JujuPy [providers/openstack/credentials.py])
 * "project-name": OS_TENANT_NAME (but also NOVA_PROJECT_NAME, NOVA_PROJECT_ID)
 * "authorized-keys": not part of the credentials, and I assume it's already supported (documenting it for the sake of completeness)