test: add fence-image-self-test

test: add fence-image-self-test

Tests that fence_malloc and fence_image_create_bits actually work: that
out-of-bounds and out-of-row (unused stride area) accesses trigger
SIGSEGV.

If fence_malloc is a dummy (FENCE_MALLOC_ACTIVE not defined), this test
is skipped.

Changes in v2:

- check FENCE_MALLOC_ACTIVE value, not whether it is defined
- test that reading bytes near the fence pages does not cause a
  segmentation fault

Changes in v3:

- Do not print progress messages unless VERBOSE environment variable is
  set. Avoid spamming the terminal output of 'make check' on some
  versions of autotools.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Ben Avison <bavison@riscosopen.org>