Always fail a system test if crashes are detected

Always fail a system test if crashes are detected

In certain situations (e.g. a named instance crashing upon shutdown in a
system test which involves shutting down a server and restarting it
afterwards), a system test may succeed despite a named crash being
triggered.  This must never be the case.  Extend run.sh to mark a test
as failed if core dumps or log lines indicating assertion failures are
detected (the latter is only an extra measure aimed at test environments
in which core dumps are not generated; note that some types of crashes,
e.g. segmentation faults, will not be detected using this method alone).

(cherry picked from commit 7706f22924dac215e22d4be4322f89814041a3a8)