sort $vhost_cfg_append hash in vhost_footer.erb template

This is so the paremter ordering in the configuration is stable. It also
force the :allow key (if it exists) to be first in the sort ordering.
It would probably be better to change `$vhost_cfg_append` into an array
of one key hashes but would require a public API change.

I'm not intending this PR to actually get merged as several other defines have similar problems.  I'd like to know if they should all be fixed in a similar, if a bit ugly, manner or if a PR to change the API would be accepted.