LU-14992 mdt: restore mkdir VBR support

LU-14992 mdt: restore mkdir VBR support

The patch of LU-14470 (striped mkdir replay by client request) broke
the mkdir VBR support: in mkdir replay, if target exists, it should
do version check instead of return -EEXIST directly, otherwise the
VBR support is broken.

Fixes: a2e997f0be ("LU-14470 dne: striped mkdir replay by client request")
Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I858499f3ef5315bbce9538733400cf6102675e4c
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55714
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>