Tests: Add LiveViewer to lttngtest environment

Tests: Add LiveViewer to lttngtest environment

Drawbacks
=========

With the current python bindings, the relayd seems to leak a file
descriptor; however, this doesn't stop the tests from working.

E.g.

```
ok 1 - BT2 live viewer exited successfully

Change-Id: I13994f7c8b0b6cffcee0d0ea0f8fca22538de651
---
  duration_ms: 1097.302968
...

 Killing session daemon (pid = 3340512)
Session daemon killed
lttng-relayd: Error: A file descriptor leak has been detected: 1
tracked file descriptors are still being tracked
```

Change-Id: Ie4294dd7238d4b6074af2d4cf193e1ca9949a741
Signed-off-by: Kienan Stewart <kstewart@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>