Channel rotate pipe between sessiond and the consumers

Channel rotate pipe between sessiond and the consumers

This new pipe is used by the consumers to inform the session daemon (in
the rotation_thread) that it has finished the rotation of a channel. In
this patch, we only setup the pipe between the daemons, it is not yet in
use.

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