lisa.tests.scheduler.load_tracking: Memoize _test_behaviour
lisa.tests.scheduler.load_tracking: Memoize _test_behaviour

Also make sure @memoized is the outermost decorator, to avoid
unnecessary trace reloading when the result is already memoized anyway.

ARM-software/lisa,credp/lisa,credp/lisa,ARM-software/lisa,credp/lisa,credp/lisa,ARM-software/lisa,ARM-software/lisa