Tests: size-based rotation: implement a trace size cutoff protection

Stop waiting for rotations when the trace exceeds a certain size cutoff.
This prevents those tests from filling a hard drive when they fail.

However, this check is racy since it is possible for an arbitrary number
of apps to run before the session daemon gets a chance to perform the
scheduled rotations.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I465462e6f1d5c17ada2b3aceb68662d8663254eb