lisa.tests.scheduler.load_tracking: Add activation duration to debug plot
lisa.tests.scheduler.load_tracking: Add activation duration to debug plot

Allow visually checking that the execution of rt-app is regular, without
sleep/activations longer than expected.

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