MDEV-18176 Galera test failure on galera.galera_gtid_slave_sst_rsync

If galera.galera_gtid_slave_sst_rsync is repeated more than once it will fail due incorrect GTID position. After stopping SLAVE node reset also GTID_SLAVE_POS variable.

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

@@ -123,6 +123,7 @@ DROP TABLE t2,t1;
 #Connection 2
 STOP SLAVE;
 RESET SLAVE ALL;
+set global gtid_slave_pos="";
 reset master;
 #Connection 3
 reset master;

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

@@ -196,6 +196,9 @@ DROP TABLE t2,t1;
 --connection node_2
 STOP SLAVE;
 RESET SLAVE ALL;
+--disable_warnings
+set global gtid_slave_pos="";
+--enable_warnings
 reset master;
 
 --echo #Connection 3