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).

Closes #1088 (closed)