Added ATHORIZED_KEYS into settings.yaml

We have two types of ssh keys:
1) system which is from /root/.ssh/id_rsa.pub
2) user defined which is set by user via web interface

Cobbler during provisioning gets user defined
ssh key from provisioning data (come from nailgun
provisioning serializer) and system ssh key directly
from /etc/cobbler/authorized_keys.

Image based provisioning is implemented as fully
data driven process. So we need system ssh public key
to come inside provisioning data and to make nailgun
able to put this key into provisioning data we need
to have this key in settings.yaml.

Besides there is a PR to fuel-library. This patch is
about putting system ssh public key into settings.yaml
during master node deployment. For details see
https://review.openstack.org/#/c/127158/

Change-Id: If3d44903cb8f1ca6636041905dc269edf5088494
Implements: blueprint image-based-provisioning
Closes-Bug: 1378832
Merge "Added ATHORIZED_KEYS into settings.yaml"