testcrypto.sh: run in TMPDIR if possible

testcrypto.sh: run in TMPDIR if possible

Avoid creating any temporary files in the current workdir.

Additional/changing files in the bin/tests/system directory are
problematic for pytest/xdist collection phase, which assumes the list of
files doesn't change between the collection phase of the main pytest
thread and the subsequent collection phase of the xdist worker threads.

Since the testcrypto.sh is also called during pytest initialization
through conf.sh.common (to detect feature support), this could
occasionally cause a race condition when the list of files would be
different for the main pytest thread and the xdist worker.

(cherry picked from commit 61330a7863c0dfe65f3add97bd363ec4998066aa)