scheduler: Update priority penalty computation in debug dump
scheduler: Update load of idle cores

In order to keep the scheduler tickless core load is computed and updated
only during various scheduler events (i.e. thread enqueue, reschedule, etc).
The problem it creates is that if a core becomes idle its load may remain
outdated for an extended period of time thus resulting in suboptimal thread
migration decisions.

The solution to this problem is to add a timer each time an idle thread is
scheudled which, after kLoadMeasureInterval, would fire and force load
update.
scheduler: Always update core heaps after thread migration

The main purpose of this patch is to eliminate the delay between thread
migration and result of that migration being visible in load statistics.
Such delay, in certain circumstances, may cause some cores to become
overloaded because the scheduler migrates too many threads to them before
the effect of migration becomes apparent.
scheduler: Inherit estimated load, do not inherit assigned core

The initial core assignment has to be done without any knowledge about
the thread behaviour. Moreover, short lived tasks may spent most of their
time executing on that initial core. This patch attempts to improve the
qualiti of that initial decision.
kernel: Adjust load tracking interval