Add a new openssh.known_hosts state

This state manages /etc/ssh/ssh_known_hosts and fills it with
public SSH host keys of other minions.

openssh/known_hosts.sls

@@ -0,0 +1,16 @@
+{% from "openssh/map.jinja" import openssh with context %}
+
+ensure dig is available:
+  pkg.installed:
+    - name: {{ openssh.dig_pkg }}
+
+manage ssh_known_hosts file:
+  file.managed:
+    - name: {{ openssh.ssh_known_hosts }}
+    - source: salt://openssh/files/ssh_known_hosts
+    - template: jinja
+    - user: root
+    - group: root
+    - mode: 644
+    - require:
+      - pkg: ensure dig is available