tests: Accept any core if no core with the "correct" pid can be found.

tests: Accept any core if no core with the "correct" pid can be found.

In some containers our view of pids is confused. We see the container
pid namespace, but the core is generated using the host pid namespace.
Since tests are run in a new fresh directory any core here is most like
is ours.

Signed-off-by: Mark Wielaard <mark@klomp.org>