Updater temp files not being cleaned up.

INFRA-683 describes complaint from Infra that tmp folder is getting filled up.
Part of the files are updater files:
rw-r-r- 1 hudson hudson 215 Aug 25 10:03 updater-execution4338849665382204507.log.tmp
rw-rr- 1 hudson hudson 215 Aug 15 10:01 updater-execution4404365778419423811.log.tmp

These files seems to be created in engine/src/main/java/org/onehippo/repository/update/UpdaterExecutionReport.java.
These files should have deleteOnExit() set.
If these files contain relevant information then it must be written to the appropriate log system.