add support for installing salt-ssh and managing the roster file, updated README and pillar.example

salt/ssh.sls

@@ -0,0 +1,13 @@
+{% from "salt/package-map.jinja" import pkgs with context %}
+
+ensure salt-ssh is installed:
+  pkg.installed:
+    - name: {{ pkgs['salt-ssh'] }}
+
+ensure roster config:
+  file.managed:
+    - name: {{ pkgs.get('config_path', '/etc/salt') }}/roster
+    - source: salt://salt/files/roster.jinja
+    - template: jinja
+    - require:
+      - pkg: ensure salt-ssh is installed