The first step in all existing setup.sh scripts is to call clean.sh. To
reduce code duplication and ensure all system tests added in the future
behave consistently with existing ones, invoke clean.sh from run.sh
before calling setup.sh.
For all system tests utilizing named instances, call clean.sh from each
test's setup.sh script in a consistent way to make sure running the same
system test multiple times using run.sh does not trigger false positives
caused by stale files created by previous runs.
Ideally we would just call clean.sh from run.sh, but that would break
some quirky system tests like "rpz" or "rpzrecurse" and being consistent
for the time being does not hurt.
