Fixes: https://pagure.io/koji/issue/527
Before path sections were expected to have zero-based numbering. If some
item was missing, parsing ended there.
Now we are more benevolent and we pick all path\d+ sections and sort
them by ordering number.
With --new-chroot, /tmp is set up as a tmpfs mount, which does not persist,
so using /builddir instead.
Related: #482 (but not a fix)
https://pagure.io/koji/issue/482
This is a different take at https://pagure.io/koji/pull-request/45
Instead of installing just the runroot builder plugin explicitly, here we
separate the plugins out into hub and builder plugins explicitly and install
each type in turn.
