Add support for ssh_auth_sources.absent

Fixes: 150

pillar.example

     # than inline in pillar, this works.
     ssh_auth_sources:
       - salt://keys/buser.id_rsa.pub
+    ssh_auth_sources.absent:
+      - salt://keys/deleteduser.id_rsa.pub # PUBLICKEY_FILE_TO_BE_REMOVED
     # Manage the ~/.ssh/config file
     ssh_known_hosts:
       importanthost:

users/init.sls

 {% endfor %}
 {% endif %}
 
+{% if 'ssh_auth_sources.absent' in user %}
+{% for pubkey_file in user['ssh_auth_sources.absent'] %}
+users_ssh_auth_source_{{ name }}_{{ loop.index0 }}:
+  ssh_auth.absent:
+    - user: {{ name }}
+    - source: {{ pubkey_file }}
+    - require:
+        - file: users_{{ name }}_user
+        - user: users_{{ name }}_user
+{% endfor %}
+{% endif %}
+
 {% if 'ssh_auth.absent' in user %}
 {% for auth in user['ssh_auth.absent'] %}
 users_ssh_auth_delete_{{ name }}_{{ loop.index0 }}: