tests: preload: Many fixes
tests: preload: Many fixes

- do not use tst_warn()

  Since it's statically linked to the test binary and calling it from
  the preload caused all kinds of linker problems.

- add reallocarray()

- make sure memory returned from calloc is zeroed

+ better debug output

Signed-off-by: Cyril Hrubis <b1e90efd3b808b8e0bcf2a9a55fd8b9a779bfd81@ucw.cz>

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