simplify the args passed to plugin hooks:

 prerepo(conf, repo, stats)
 prebuild(conf, aport, progress)
 postbuild(conf, aport, success)
 postrepo(conf, repo, stats)

By passing over conf we reduce number of args passed to hook function
and we make it possible to set config options in
/etc/buildrepo/config.lua that is passed on to the hook. This is useful
for setting things like mqtt broker, url prefix for buildlogs and
similar.

this is so we can simplify the args passed to plugins

and make it possible to override in config

This is so we will catch errors when there are circular dependencies and
get the error triggered when trying to build the package. Otherwise the
packages will not be built at all and warning easily gets unnoticed.

For example rust -> cargo -> rust