Clean-up: lttng: check status returned when checking rotation state

While the use of the destruction handle in the lttng client guarantees
that obtaining the rotation's state will succeed, it is a poor example
to give of using this API. Moreover, we don't wait to give the
impression that this could never change.

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