lib: introduce test_meminit module

lib: introduce test_meminit module

Add tests for heap and pagealloc initialization.  These can be used to
check init_on_alloc and init_on_free implementations as well as other
approaches to initialization.

Expected test output in the case the kernel provides heap initialization
(e.g.  when running with either init_on_alloc=1 or init_on_free=1):

  test_meminit: all 10 tests in test_pages passed
  test_meminit: all 40 tests in test_kvmalloc passed
  test_meminit: all 60 tests in test_kmemcache passed
  test_meminit: all 10 tests in test_rcu_persistent passed
  test_meminit: all 120 tests passed!

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Alexander Potapenko <[email protected]>
Acked-by: Kees Cook <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Kostya Serebryany <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Sandeep Patil <[email protected]>
Cc: Laura Abbott <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Marco Elver <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>