Pass the loop to MAKE_VALGRIND_HAPPY() so it's explicit on which loop
needs to be cleaned up. Since it asserts on uv_loop_close(), need to
remove a couple of those that were being done before the call.
Cleanup where loop was assigned, so the entire test either uses loop or
uv_default_loop(). Not both.
Also take care of any reqs that may have been left uncleaned.
`uv_try_write(stream, buf, size)` acts like `uv_write()`,
but without queueing actual write until UV_POLLOUT (or IOCP completion).
This is useful for doing writes using on-stack `uv_write_t` requests.
fix#1025
