[lit] Fix tests on Windows

max-time.py:
  Windows does not have a native `sleep` command, use `time.sleep()` in
  Python instead.

max-failures.py:
  The max-failure test reused the shtest-shell test inputs instead of
  defining its own "test domain".  However, the output of this
  shtest-shell "test domain" is slightly different on Windows, which now
  bites us since we made the max-failures test stricter.  Let's define
  our own "max failures" test domain.