Fix: relayd should listen for viewers on localhost only by default

Having relayd listening by default on 0.0.0.0 (all interfaces) with a
protocol without authentication is an information leak waiting to
happen.

Users should explicitely specify if they want to listen on all
interfaces, using e.g. -L tcp://0.0.0.0:5344 (see lttng-relayd(8)
manpage for details). They should only do so if they use a firewall, or
are within a secured network.

Fixes #746

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: improve lttng with live by spawning relayd

The create --live, will try to spawn a default relayd if no URL is
given.

The lttng view now supports the live tracing mode thus lttng view is
usable with a live session.

Fixes #738

Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: Unchecked session pointer when destroying a connection in relayd

An unknown command currently crashes the relay daemon since
destroy_connection calls destroy_session without checking whether or not
a session is associated with the connection.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>