test: add a test for the same mroonga_log_file value case

mysql-test/mroonga/storage/variable/log_file/r/same_value.result

@@ -0,0 +1,4 @@
+SET GLOBAL mroonga_log_file = "groonga.log";
+SHOW GLOBAL VARIABLES LIKE 'mroonga_log_file';
+Variable_name	Value
+mroonga_log_file	groonga.log

mysql-test/mroonga/storage/variable/log_file/t/same_value.test

@@ -0,0 +1,22 @@
+# Copyright(C) 2014 Kouhei Sutou <kou@clear-code.com>
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+--source ../../../../include/mroonga/have_mroonga.inc
+
+SET GLOBAL mroonga_log_file = "groonga.log";
+SHOW GLOBAL VARIABLES LIKE 'mroonga_log_file';
+
+--source ../../../../include/mroonga/have_mroonga_deinit.inc