MDEV-15662 mariabackup.huge_lsn fails sporadically with "log sequence number is in the future"

- Problem is that test case creates iblogfile* files. So existing
ibdata pages could point to future LSN. Fix is that taking the
backup of data before iblogfile* creation and apply it before
exiting the test case.

mysql-test/suite/mariabackup/huge_lsn.result

@@ -17,3 +17,7 @@ SELECT * FROM t;
 i
 1
 DROP TABLE t;
+# shutdown server
+# remove datadir
+# xtrabackup move back
+# restart server

mysql-test/suite/mariabackup/huge_lsn.test

@@ -9,6 +9,10 @@ let INNODB_PAGE_SIZE=`select @@innodb_page_size`;
 let MYSQLD_DATADIR=`select @@datadir`;
 call mtr.add_suppression("InnoDB: New log files created");
 
+let $targetdir_old=$MYSQLTEST_VARDIR/tmp/backup_1;
+--disable_result_log
+exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf --backup --target-dir=$targetdir_old;
+--enable_result_log
 --source include/shutdown_mysqld.inc
 
 perl;
@@ -52,3 +56,7 @@ exec $XTRABACKUP  --prepare --target-dir=$targetdir;
 SELECT * FROM t;
 DROP TABLE t;
 rmdir $targetdir;
+let $targetdir= $targetdir_old;
+exec $XTRABACKUP --prepare --target-dir=$targetdir;
+--source include/restart_and_restore.inc
+rmdir $targetdir_old;