subprocess: close pipes/fds by using ExitStack (GH-11686)

Close pipes/fds in subprocess by using ExitStack.

"In case of premature failure on X.Close() or os.close(X) the remaining pipes/fds will remain "open". Perhaps it makes sense to use contextlib.ExitStack."
- Rationale: https://github.com/python/cpython/pull/11575#discussion_r250288394