Test: Refine annotaion and testcase for poll.

1. Add more detail info to make the purpose and process
of the test cases more clear which include test goal,
test step, input, judging criteria, constraints, etc.,
and these can be seen in our Zephyr documentations.
2. Add some negative test code.

Signed-off-by: YouhuaX Zhu <youhuax.zhu@intel.com>