This prevents tracebacks during shutdown:

  Unhandled exception in thread started by <bound method Thread.__bootstrap of <Thread(Thread-1, stopped daemon 139820471113472)>>
  Traceback (most recent call last):
    File "soft/lib/python2.7/threading.py", line 774, in __bootstrap
      self.__bootstrap_inner()
    File "soft/lib/python2.7/threading.py", line 814, in __bootstrap_inner
      (self.name, _format_exc()))
    File "soft/lib/python2.7/traceback.py", line 242, in format_exc
      return ''.join(format_exception(etype, value, tb, limit))
    File "soft/lib/python2.7/traceback.py", line 141, in format_exception
      list = list + format_tb(tb, limit)
    File "soft/lib/python2.7/traceback.py", line 76, in format_tb
      return format_list(extract_tb(tb, limit))
    File "soft/lib/python2.7/traceback.py", line 100, in extract_tb
      linecache.checkcache(filename)
  TypeError: 'NoneType' object is not callable

Also rename the method because this is not longer Zserver.

This waitress close() API is not public part of API, so we still ignore the case where the server thread does not stop after 5 seconds. This happens if some HTTP connections are still open at the end of test.