Merge pull request #263 from robruma/feature/support_master_id_option

Adding support for master_id option

salt/files/master.d/f_defaults.conf

 # after the comment then the value is presented as an example and is not the
 # default.
 
+# The id to be passed in the publish job to minions.
+# This is used for MultiSyndics to return the job to the requesting master.
+# This must be the same string as the syndic is configured with.
+# master_id: None
+{{ get_config('master_id', 'None') }}
+
 # Per default, the master will automatically include all config files
 # from master.d/*.conf (master.d is a directory in the same directory
 # as the main master config file).