MDEV-6699: wsrep_node_name not automatically set to hostname

Update sys_vars.sysvars_wsrep test.

mysql-test/suite/sys_vars/r/sysvars_wsrep.result

@@ -311,9 +311,9 @@ READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	WSREP_NODE_NAME
 SESSION_VALUE	NULL
-GLOBAL_VALUE	
+GLOBAL_VALUE	HOSTNAME
 GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	
+DEFAULT_VALUE	HOSTNAME
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	VARCHAR
 VARIABLE_COMMENT	Node name

mysql-test/suite/sys_vars/t/sysvars_wsrep.test

 --source include/have_wsrep.inc
 --source include/word_size.inc
 --let $datadir = `SELECT @@datadir`
+--let $hostname = `SELECT @@hostname`
 
---replace_result $datadir DATADIR
+--replace_result $datadir DATADIR $hostname HOSTNAME
 --vertical_results
 select * from information_schema.system_variables
   where variable_name like 'wsrep%'