shared.cfg: Update live_snapshot_chain commands for Windows guests

dir command from Windows guests will include summary of current
directory informations. Which will change as we use the system disk
in test. So update the command to ignore the summary lines.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #1532 from ypu/snapshot

shared.cfg: Update live_snapshot_chain commands for Windows guests