os.linux: Make the priority of the KernelState available as an Aspect

os.linux: Make the priority of the KernelState available as an Aspect

Since bug 460635 points into the direction of using aspects for the
properties view, I think it makes sense to create a ThreadPriorityAspect
making the priority tracked in the KernelState vaialable as an aspect.

Change-Id: Icf3ed0a03fd9f6e993465bc1c155c185e058de54
Signed-off-by: Christian Mansky <christian.mansky@gmx.at>
Reviewed-on: https://git.eclipse.org/r/42884
Reviewed-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Reviewed-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>