amend! Port the long TCP stream test to Python

amend! Port the long TCP stream test to Python

Port the long TCP stream test to Python

Previously, the packet.pl script was used to send the a series of frames
to named; this worked by accident as most of these were refused by the
kernel with EAGAIN. packet.pl prints a dot every 1000 packets, so this
slowed the script down and allowed some frames to get through.

Reimplement the test in Python: build the packet with dnspython, send
~6 MiB of data over TCP discarding all replies and then check if the
server is still alive.