bpo-30106: Fix test_asyncore.test_quick_connect() (#1234)

bpo-30106: Fix test_asyncore.test_quick_connect() (#1234)

test_quick_connect() runs a thread up to 50 seconds, whereas the
socket is connected in 0.2 second and then the thread is expected to
end in less than 3 second. On Linux, the thread ends quickly because
select() seems to always return quickly. On FreeBSD, sometimes
select() fails with timeout and so the thread runs much longer than
expected.

Fix the thread timeout to fix a race condition in the test.