ctf: Add advanced trace tests

ctf: Add advanced trace tests

Using a more exotic test trace.

I'm not exactly sure why a string field ends up in-between the variant
selector and its value, but this is how they are printed by Babeltrace,
so I assume we're doing the right thing.

Change-Id: I4bd0f35d31a7c592fafd64b3321f182f9de71c79
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/17550