added test case galera_ist_mariabackup

mysql-test/suite/galera/r/galera_ist_mariabackup.cnf

+!include ../galera_2nodes.cnf
+
+[mysqld]
+wsrep_sst_method=mariabackup
+wsrep_sst_auth=root:
+
+[mysqld.1]
+wsrep_provider_options='base_port=@mysqld.1.#galera_port;pc.ignore_sb=true'
+
+[mysqld.2]
+wsrep_provider_options='base_port=@mysqld.2.#galera_port;pc.ignore_sb=true'
+

mysql-test/suite/galera/r/galera_ist_mariabackup.test

+--source include/big_test.inc
+--source include/galera_cluster.inc
+--source include/have_innodb.inc
+--source include/have_mariabackup.inc
+
+--source suite/galera/include/galera_st_disconnect_slave.inc
+--source suite/galera/include/galera_st_shutdown_slave.inc
+
+--source suite/galera/include/galera_st_kill_slave.inc
+--source suite/galera/include/galera_st_kill_slave_ddl.inc