Big cleanup of network live

Sync with the babeltrace tree to use the same code base for network live
streaming.

Use :
$ lttngtop -r net://localhost
to list the sessions on localhost and then
$ lttngtop -r net://localhost/42
to attach to session 42 on localhost for example.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>