MDEV-10823 amend : Use opt_log_basename instead of hostname to test

filesystem case sensitivity.

Hostname can include characters, which are invalid for use as filename,
thus case sensitivity test will fail to produce meaningful results.

sql/mysqld.cc

@@ -9887,9 +9887,9 @@ static int test_if_case_insensitive(const char *dir_name)
   MY_STAT stat_info;
   DBUG_ENTER("test_if_case_insensitive");
 
-  fn_format(buff, glob_hostname, dir_name, ".lower-test",
+  fn_format(buff, opt_log_basename, dir_name, ".lower-test",
 	    MY_UNPACK_FILENAME | MY_REPLACE_EXT | MY_REPLACE_DIR);
-  fn_format(buff2, glob_hostname, dir_name, ".LOWER-TEST",
+  fn_format(buff2, opt_log_basename, dir_name, ".LOWER-TEST",
 	    MY_UNPACK_FILENAME | MY_REPLACE_EXT | MY_REPLACE_DIR);
   mysql_file_delete(key_file_casetest, buff2, MYF(0));
   if ((file= mysql_file_create(key_file_casetest,