Back porting the test case for semi-sync

mysql-test/include/have_semisync_plugin.inc

+#
+# Check if dynamic loading is supported
+#
+--require r/have_dynamic_loading.require
+disable_query_log;
+show variables like 'have_dynamic_loading';
+enable_query_log;
+
+#
+# Check if the variable SEMISYNC_MASTER_PLUGIN is set
+#
+if (`select LENGTH('$SEMISYNC_MASTER_PLUGIN') = 0`)
+{
+  skip Need semisync plugins;
+}

mysql-test/suite/rpl/t/rpl_semi_sync-master.opt

+$SEMISYNC_PLUGIN_OPT

mysql-test/suite/rpl/t/rpl_semi_sync-slave.opt

+$SEMISYNC_PLUGIN_OPT