fix(macros.jinja): use user kwarg for schemas (required on FreeBSD)

* Not available in `2017.7`:
  - https://docs.saltstack.com/en/2017.7/ref/states/all/salt.states.postgres_schema.html

Author: myii

postgres/macros.jinja

@@ -18,7 +18,8 @@
   {%- if 'ensure' in kwarg %}
     {%- set ensure = kwarg.pop('ensure') %}
   {%- endif %}
-  {%- if 'user' not in kwarg and state != 'postgres_schema' %}
+  {%- set user_available = False if (state == 'postgres_schema' and grains.saltversioninfo < [2018, 3]) else True %}
+  {%- if 'user' not in kwarg and user_available %}
     {%- do kwarg.update({'user': postgres.user}) %}
   {%- endif -%}