tests: add helpers.h to harden the tests

As axboe said, Right now a lot of basic stuff is duplicated,
and it makes the tests bigger than they should be.
Here, we try to add helpers.h which will contains various
utilities that tests could use, then that'd help make tests simpler.

In this patch, we just add one helper io_uring_malloc(), which
will call assert() if allocating memory fails.
We will add more helpers in subsequent patches

Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
28 files changed