Add verify_master_pubkey_sign

salt/files/minion.d/f_defaults.conf

 # master check alive interval
 {{ get_config('master_alive_interval', '30') }}
 
+# verify_master_pubkey_sign
+{{ get_config('verify_master_pubkey_sign', 'False') }}
+
 # include extra config
 {% if 'include' in cfg_minion -%}
     {% if isinstance(cfg_minion['include'], list) -%}