test/stack: check errors for multi-threads

test/stack: check errors for multi-threads

Use rte_eal_wait_lcore to wait and get the return value for all cores.
This is used to propagate any error to the main core.

Signed-off-by: Steven Lariau <steven.lariau@arm.com>
Reviewed-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Gage Eads <gage.eads@intel.com>