selftest: Make dns_hub socket timeout match DNS_REQUEST_TIMEOUT

selftest: Make dns_hub socket timeout match DNS_REQUEST_TIMEOUT

I was hitting the recv_packet = s.recv(2048, 0) exception because
the socket timeout was reached. We've seen it before, but it seemed more
common after changing the default process-model to prefork. This patch
makes the socket timeout used by the python code consistent with the C
code.

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>