tests/test-empty-dir.t

automation: always use latest Windows AMI

The old AMI isn't available any more.

We seem to run into this problem every few months. Amazon (or
Microsoft) appears to be removing the old AMIs when they are
superseded or something. Let's give up on tracking known images
and switch the image selection logic to use the latest published
image.

Differential Revision: https://phab.mercurial-scm.org/D8465

  $ hg init

  $ echo 123 > a
  $ hg add a
  $ hg commit -m "first" a

  $ mkdir sub
  $ echo 321 > sub/b
  $ hg add sub/b
  $ hg commit -m "second" sub/b

  $ cat sub/b
  321

  $ hg co 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ cat sub/b 2>/dev/null || echo "sub/b not present"
  sub/b not present

  $ test -d sub || echo "sub not present"
  sub not present