os.linux: Correctly model each CPU's run queue

os.linux: Correctly model each CPU's run queue

Add a new attribute to the kernel state system:

THREADS
 +--1000
     +--Current_cpu_rq

Which will track on which CPU's run queue this thread
is currently located. Unlike the cpu -> Current_thread
attribute, several threads can be present on the same
CPU's run queue at the same time.

This will allow for example tracking on which CPU a
thread is expecting to go when it is in the WAIT_FOR_CPU
state.

This requires tweaks to the sched_switch, sched_wakeup
and process_fork handlers, as well as adding a new handler
for the sched_migrate_task event (which simply moves a
non-running thread from one run queue to another).

Change-Id: I6e0386214df195eb6389cec87f2e6a42fdc0691d
Signed-off-by: Alexandre Montplaisir <alexmonthy@efficios.com>