DRY: Centralize Logfile Redirections in Integration Test Cases

This eliminates the omnipresent logfile redirections in the integration test scripts (`foo >> $logfile 2>&1`) and centralizes them in `./run.sh`. In some cases the `$logfile` variable might still be useful and is passed to the test case as before. Although I suggest the general convention, that all output through *stdout* and *stderr* produced by a test case ends up in the test log file by default.