test: remove bad tcp_write_error test
It makes the assumption that if you try to write to a localhost socket
often enough, eventually its send queue will fill up - which doesn't
happen if the machine it's running on is fast enough.
test: move loop cleanup code to the individual tests
Tests: make test-tcp-write-error pass on XP
fix tcp_write_error for windows
test: check that write_queue_size updates after write error