Fix: leak of streams

Streams can be added when we attach to a session and if new streams are
added while the session is running. We were overriding the session
streams array in get_new_stream, so at teardown we could leak the
streams that were added before that call. We now keep a list of all the
streams in the session and add each stream in that list in both code
paths.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>