Fix/disable some failing galera tests.

Author: Nirbhay Choubey

mysql-test/suite/galera/disabled.def

@@ -30,5 +30,8 @@ galera_gcs_fragment : Incorrect arguments to SET
 galera_flush_local : Fails sporadically
 galera_binlog_stmt_autoinc : TODO: investigate
 galera_concurrent_ctas : Test times out, investigate
+MW-286 : TODO: investigate
 galera_sst_xtrabackup-v2-options : TODO: Fix test case
+galera_sst_xtrabackup-v2 : TODO: Fix test case
+galera_sst_xtrabackup-v2_encrypt_with_key : TODO: Fix test case
 mysql-wsrep#33 : TODO: investigate