Current code wrote a single valgrind.log in the top-level directory.
This was overwritten with each valgrinded program, which wasn't much
use. The new version writes multiple separate valgrind-*.log files
containing the date and PID (so each is unique).
It would nice if valgrind could delete log files that don't contain
errors, but this doesn't appear to be possible.
Having a separate directory means:
(1) It's easy to clean up orphaned temporary files, the appliance,
etc.
(2) You can put an SELinux label on this directory so that qemu can
write to it when you're using sVirt and SELinux is enforcing:
chcon --reference=/tmp tmp
