add templated file for reactor configuration and update pillar.example.

pillar.example

       - IAD
       - SYD
       - HKG
+  reactor:
+    - 'deploy':
+      - /srv/salt/reactors/deploy.sls
 
 salt_cloud_certs:
   aws:

salt/files/master.d/reactor.conf

+#
+# This file is managed by Salt! Do not edit by hand!
+#
+{%- set reactors = salt['pillar.get']('salt:reactor') -%}
+{%- if reactors %}
+reactor:
+{%- for reactor in reactors %}
+{%- for event_tag, reactor_files in reactor.items() %}
+  - '{{ event_tag }}'
+{%- for reactor_file in reactor_files %}
+    - {{ reactor_file }}
+{%- endfor %}
+{%- endfor %}
+{% endfor -%}
+{%- endif -%}