This change extends the existing in-tree test infrastructure such
that it can also be run as part of a the installed package. This
simplifies testing on multiple systems and is generally all around
useful. The scripts may still be run in-tree and will use the
in-tree build products as long as .script-config exists.
argument is available. This flags argument was added to allow a clean
API for disabling prefetch, so I'll update zpios to use it in preference
to the module option hack used before.