salt: use repo.saltstack.com

apt/repository/saltstack.sls

+saltstack-repo:
+  pkgrepo.managed:
+    - humanname: repo.saltstack.com
+{%- if grains['osfinger'] == 'Debian-9' %}
+    - name: deb http://repo.saltstack.com/apt/debian/8/amd64/latest jessie main
+{%- else %}
+    - name: deb http://repo.saltstack.com/apt/debian/9/amd64/latest stretch main
+{%- endif %}
+    - file: /etc/apt/sources.list.d/saltstack.list
+    - key_url: https://repo.saltstack.com/apt/debian/9/amd64/latest/SALTSTACK-GPG-KEY.pub
+    - require:
+      - pkg: python-apt

salt/master.sls

+salt-master:
+  pkg.installed:
+    - fromrepo: saltstack-repo
+
 /etc/ferm/conf.d/40-salt-zmq.conf:
   file.managed:
     - source: salt://salt/files/ferm.conf
     - user: root
     - group: root
     - mode: 644
-

salt/minion.sls

 salt-minion:
+  pkg.installed:
+    - fromrepo: saltstack-repo
   service.running:
     - enable: True
     - watch: