libarchive: skip fuzz tests in ptest run

libarchive: skip fuzz tests in ptest run

The libarchive fuzz tests (test_fuzz_ar, test_fuzz_cab, test_fuzz_cpio,
test_fuzz_iso9660, ...) run 1000 randomised iterations per archive format
and are intended for dedicated fuzzing infrastructure rather than routine
ptest execution. On the time and memory constrained autobuilder QEMU
targets they regularly time out, e.g.:

  158: test_fuzz_iso9660    Timeout! System state:

Upstream provides the SKIP_TEST_FUZZ environment variable to skip these
tests. Export it from run-ptest so the fuzz tests are skipped rather than
run, while the rest of the test suite continues to execute normally.

[YOCTO #16340]

Signed-off-by: Siva Balasubramanian <sivakumar.bs@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>