Live unit test

Live unit test

The actual test :
- connect to the relayd on localhost
- list the sessions (should find only one)
- attach to the first session
- receive all the streams
- get all the metadata
- get one index per stream
- get one data packet

Then the session is stopped, destroyed and the daemons killed.

Two tests are also added just to for the lttng commands with a --live
session.

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