test-coroutine: test cost introduced by coroutine

test-coroutine: test cost introduced by coroutine

This test runs dummy function with coroutine by using
two enter and one yield since which is a common usage.

So we can see the cost introduced by corouting for running
one function, for example:

	Run operation 20000000 iterations 4.841071 s, 4131K operations/s
	242ns per coroutine

Signed-off-by: Ming Lei <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>