Fix the handling of event_return_whitelist/event_return_blacklist

If those options are set in pillar data, the jinja template
salt/files/master.d/_defaults.conf would fail to compile trying to
evaluate non-existing variables.

Replace those variables with the corresponding dictionnary entries.

salt/files/master.d/_defaults.conf

@@ -150,12 +150,12 @@
 # Only events returns matching tags in a whitelist
 {% if 'event_return_whitelist' in cfg_master -%}
 event_return_whitelist:
-  {%- for event_return in event_return_whitelist %}
+  {%- for event_return in cfg_master['event_return_whitelist'] %}
   - {{ event_return }}
   {%- endfor -%}
 {% elif 'event_return_whitelist' in cfg_salt -%}
 event_return_whitelist:
-  {%- for event_return in event_return_whitelist %}
+  {%- for event_return in cfg_salt['event_return_whitelist'] %}
   - {{ event_return }}
   {%- endfor -%}
 {% else -%}
@@ -167,12 +167,12 @@ event_return_whitelist:
 # Store all event returns _except_ the tags in a blacklist
 {% if 'event_return_blacklist' in cfg_master -%}
 event_return_blacklist:
-  {%- for event_return in event_return_blacklist %}
+  {%- for event_return in cfg_master['event_return_blacklist'] %}
   - {{ event_return }}
   {%- endfor -%}
 {% elif 'event_return_blacklist' in cfg_salt -%}
 event_return_blacklist:
-  {%- for event_return in event_return_blacklist %}
+  {%- for event_return in cfg_salt['event_return_blacklist'] %}
   - {{ event_return }}
   {%- endfor -%}
 {% else -%}