Handle file_recv option

Handle this option to allow/deny a minion to push
a file up to the master server (disabled by default).

Change-Id: I08f9bfedbc5356442c314992326dd206484e34ab

salt/files/master.conf

@@ -177,6 +177,8 @@ nacl.config:
   {%- endif %}
 {%- endif %}
 
+file_recv: {{ master.get('file_recv', False) }}
+
 {#-
 vim: syntax=jinja
 -#}