ci: catch coredumps

Parts of the unit tests code rely on forked/secondary processes
(expectedly) failing.
A crash in those situations could be missed so add a check on coredumps
presence after unit tests have run.
When unit tests fail, it can also help checking for coredumps as it
could give more insights on what happened.

In some situations (like explicit call to rte_panic), coredump generation
must be disabled to avoid false positives.

Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Luca Boccassi <bluca@debian.org>
Acked-by: Aaron Conole <aconole@redhat.com>