Salt: support systemd (don't assume Redhat <=> systemd)

Also work around problems with Salt & systemd services, in particular
that Salt doesn't issue a daemon-reload.

cluster/saltbase/pillar/systemd.sls

@@ -0,0 +1,9 @@
+{% if grains['oscodename'] in [ 'vivid', 'jessie' ] %}
+is_systemd: True
+systemd_system_path: /lib/systemd/system
+{% elif grains['os_family'] == 'RedHat' %}
+is_systemd: True
+systemd_system_path: /usr/lib/systemd/system
+{% else %}
+is_systemd: False
+{% endif %}

cluster/saltbase/pillar/top.sls

@@ -5,3 +5,4 @@ base:
     - logging
     - docker-images
     - privilege
+    - systemd