Skip semisync test if the plugin-dir is not set to semisync plugin dir

mysql-test/include/have_semisync_plugin.inc

@@ -13,3 +13,10 @@ if (`select LENGTH('$SEMISYNC_MASTER_PLUGIN') = 0`)
 {
   skip Need semisync plugins;
 }
+
+#
+# Check if --plugin-dir was setup for semisync
+#
+if (`SELECT CONCAT('--plugin-dir=', @@plugin_dir) != '$SEMISYNC_PLUGIN_OPT'`) {
+  --skip SEMISYNC plugin requires that --plugin-dir is set to the semisync plugin dir (either the .opt file does not contain \$SEMISYNC_PLUGIN_OPT or another plugin is in use)
+}