test/ring: add contention stress test

test/ring: add contention stress test

Introduce stress test for ring enqueue/dequeue operations.
Performs the following pattern on each slave worker:
dequeue/read-write data from the dequeued objects/enqueue.
Serves as both functional and performance test of ring
enqueue/dequeue operations under high contention
(for both over committed and non-over committed scenarios).

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>