fstests: btrfs/271: specify "-m raid1" to avoid false alerts

fstests: btrfs/271: specify "-m raid1" to avoid false alerts

[FALSE FAILURE]
Test case btrfs/271 will fail like the following, if the MKFS_OPTIONS
has specified a metadata profile (either SINGLE or DUP):

  btrfs/271 1s ... - output mismatch (see /home/adam/xfstests/results//btrfs/271.out.bad)
      --- tests/btrfs/271.out	2022-11-07 09:59:11.256666666 +1030
      +++ /home/adam/xfstests/results//btrfs/271.out.bad	2025-04-17 19:49:00.129443427 +0930
      @@ -1,523 +1,9 @@
       QA output created by 271
       Allow global fail_make_request feature
       Step 1: writing with one failing mirror:
      -wrote 8192/8192 bytes at offset 0
      -XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
      +fsync: Input/output error
       Step 2: verify that the data reads back fine:
      ...
      (Run 'diff -u /home/adam/xfstests/tests/btrfs/271.out /home/adam/xfstests/results//btrfs/271.out.bad'  to see the entire diff)
  Ran: btrfs/271
  Failures: btrfs/271
  Failed 1 of 1 tests

[CAUSE]
The test case relies on mkfs.btrfs to use RAID1 as default metadata
profile if multiple devices are provided.

This is no longer true if the run has specified certain profile in
MKFS_OPTIONS.

If "-m dup" or "-m single" is specified, the fs will flip read-only as
either profile can handle any missing or failed device super block
writeback.

[FIX]
Just specify both metadata (RAID1) and data (RAID1, already in the test
case) to avoid the false failure.

Reported-by: kdevops <kdevops@lists.linux.dev>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>