selftests: cgroup: add 'malloc' failures checks in test_memcontrol

There are several 'malloc' calls in test_memcontrol, which can be
unsuccessful.  This patch will add 'malloc' failures checking to give more
details about test's fail reasons and avoid possible undefined behavior
during the future null dereference (like the one in
alloc_anon_50M_check_swap function).

Link: https://lkml.kernel.org/r/20230226131634.34366-1-ivan.orlov0322@gmail.com
Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>