Follow up fixes for making @@wsrep_provider read-only

* Remove usage of wsrep_provider variable in galera_ist_restart_joiner
* Rename galera_load_provider.inc and galera_unload_provider.inc to
  galera_stop_replication.inc and galera_start_replication.inc. Their
  original names were no longer reflecting what these include files do.

followup for ce3a2a68Reviewed-by: Jan Lindström <jan.lindstrom@mariadb.com>

mysql-test/suite/galera/include/galera_st_disconnect_slave.inc

@@ -21,7 +21,7 @@ INSERT INTO t1 VALUES ('node2_committed_before');
 INSERT INTO t1 VALUES ('node2_committed_before');
 COMMIT;
 
---source suite/galera/include/galera_unload_provider.inc
+--source suite/galera/include/galera_stop_replication.inc
 
 --connection node_1
 --let $wait_condition = SELECT VARIABLE_VALUE = 1 FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'wsrep_cluster_size'
@@ -53,7 +53,7 @@ INSERT INTO t1 VALUES ('node1_to_be_rollbacked_after');
 INSERT INTO t1 VALUES ('node1_to_be_rollbacked_after');
 
 --connection node_2
---source suite/galera/include/galera_load_provider.inc
+--source suite/galera/include/galera_start_replication.inc
 
 --let $wait_condition = SELECT VARIABLE_VALUE = 2 FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'wsrep_cluster_size'
 --source include/wait_condition.inc

mysql-test/suite/galera/r/galera_ist_restart_joiner.result

@@ -3,8 +3,9 @@ connection node_2;
 CREATE TABLE t1 (f1 INTEGER PRIMARY KEY, f2 CHAR(1));
 INSERT INTO t1 VALUES (1, 'a'), (2, 'a'), (3, 'a'), (4, 'a'), (5, 'a'),(6, 'a');
 connection node_2;
+SET SESSION wsrep_sync_wait=0;
 Unloading wsrep provider ...
-SET GLOBAL wsrep_provider = 'none';
+SET GLOBAL wsrep_cluster_address = '';
 connection node_1;
 UPDATE t1 SET f2 = 'b' WHERE f1 > 1;
 UPDATE t1 SET f2 = 'c' WHERE f1 > 2;

mysql-test/suite/galera/t/galera_ist_restart_joiner.test

@@ -21,7 +21,8 @@ INSERT INTO t1 VALUES (1, 'a'), (2, 'a'), (3, 'a'), (4, 'a'), (5, 'a'),(6, 'a');
 
 # Disconnect node #2
 --connection node_2
---source suite/galera/include/galera_unload_provider.inc
+SET SESSION wsrep_sync_wait=0;
+--source suite/galera/include/galera_stop_replication.inc
 
 --connection node_1
 UPDATE t1 SET f2 = 'b' WHERE f1 > 1;
@@ -45,7 +46,6 @@ UPDATE t1 SET f2 = 'c' WHERE f1 > 2;
 --disable_query_log
 # base_port setting is lost for some reason when unloading provider, so we need to restore it
 --eval SET GLOBAL wsrep_provider_options= 'base_port=$NODE_GALERAPORT_2';
---eval SET GLOBAL wsrep_provider = '$wsrep_provider_orig';
 # Make sure IST will block ...
 --let $galera_sync_point = recv_IST_after_apply_trx
 --source include/galera_set_sync_point.inc

mysql-test/suite/galera/t/galera_sst_mariabackup_lost_found.test

@@ -10,7 +10,7 @@
 --connection node_2
 
 #--connection node_2
-#--source suite/galera/include/galera_unload_provider.inc
+#--source suite/galera/include/galera_stop_replication.inc
 
 --echo Shutting down server ...
 --source include/shutdown_mysqld.inc

mysql-test/suite/galera_3nodes/t/galera_ipv6_mysqldump.test

@@ -37,7 +37,7 @@ SET GLOBAL wsrep_sst_method = 'mysqldump';
 #
 
 #--connection node_2
-#--source suite/galera/include/galera_unload_provider.inc
+#--source suite/galera/include/galera_stop_replication.inc
 
 --echo Shutting down server ...
 --source include/shutdown_mysqld.inc
@@ -62,7 +62,7 @@ INSERT INTO t1 VALUES (1);
 --let $start_mysqld_params = --wsrep_sst_auth=sst: --wsrep_sst_method=mysqldump --wsrep-sst-receive-address=[::1].1:$NODE_MYPORT_2
 --source include/start_mysqld.inc
 
-#--source suite/galera/include/galera_load_provider.inc
+#--source suite/galera/include/galera_start_replication.inc
 
 --let $wait_condition = SELECT VARIABLE_VALUE = 3 FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'wsrep_cluster_size'
 --source include/wait_condition.inc

mysql-test/suite/galera_3nodes/t/galera_ist_gcache_rollover.test

@@ -29,10 +29,10 @@ INSERT INTO t1 VALUES (01), (02), (03), (04), (05);
 
 # Disconnect nodes #2 and #3
 --connection node_2
---source suite/galera/include/galera_unload_provider.inc
+--source suite/galera/include/galera_stop_replication.inc
 
 --connection node_3
---source suite/galera/include/galera_unload_provider.inc
+--source suite/galera/include/galera_stop_replication.inc
 
 --connection node_1
 --source include/wait_until_connected_again.inc