cli: mimic behavior of BT1 when trying to attach to live session

cli: mimic behavior of BT1 when trying to attach to live session

In Babeltrace 1, when trying to attach to a LTTng live session the
`babeltrace` command would exit with status 0 (SUCCESS) if it
successfully connected to the relay daemon _even if_ it did not find the
requested session.

To mimic the behavior of BT1, we set the `session-not-found-action`
parameter to "end". This makes the message iterator of an lttng-live
component return a END status if the requested session is not found
on the relay daemon and makes the cli return gracefully with SUCCESS.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I3b3810f97c090d102fd30902fda37434f62d5c01