LU-15553 test: mkdir_on_mdt0 in replay-vbr.sh

LU-15553 test: mkdir_on_mdt0 in replay-vbr.sh

Change mkdir to mkdir_on_mdt0 in several replay-vbr.sh sub tests.

Lustre-change: https://review.whamcloud.com/56540
Lustre-commit: f6c733c422eae64cea93c33fb14e6adb2eed81d0

Fixes: b9c4dc3c33 ("LU-14792 llite: enable filesystem-wide default LMV")
Test-Parameters: trivial testlist=replay-vbr mdtcount=4
Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I7457c155bbadb86adf8272113a4e4202b98c20a5
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56943
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>