autodisc: improve logging

Improve the logging in the support_info_query_all_sources function:

- Include the group after a successful query
- Include the group when announcing the winner
- Format messages according to our standard, "message: key=value, ...".

Change-Id: I9833ea63314cde912c1da56d6ed2483f34783f17
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1976
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>