Fix: src.ctf.lttng-live: omitting stream end on stream hang up

Fix: src.ctf.lttng-live: omitting stream end on stream hang up

Issue
=====
When receiving a LTTNG_VIEWER_INDEX_HUP request status, a
`src.ctf.lttng-live` component quickly removes the associated stream
iterator and move on to the next request without sending the stream end
message to properly close the stream. This breaks the guarantee that
stream end messages are always present.

Solution
========
Whenever we receive an HUP status from the server, we trigger the
`bt_msg_iter` code to hit an BT_MSG_ITER_MEDIUM_STATUS_EOF so it
generates the stream end message that closes the stream.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I89924ee95b35ca62c103651ad44c9eaf71f6df53
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1840
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>