tests/func/050: fix false alarm during 'vdi check'

Now we can use nid to connect to the node, this means we can make use of io nic
if any. Dog will fallback to non-io nic when io nic is broken.

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>