Don't try and enable the runroot plugin on builders that don't have it installed.

This was causing all non runroot builders to never be ready because they
couldn't load the plugin.

roles/koji_builder/templates/kojid.conf

@@ -63,10 +63,11 @@ ca = /etc/kojid/cacert.pem
 ;certificate of the CA that issued the HTTP server certificate
 serverca = /etc/kojid/cacert.pem
 
-; Let's try the runroot plugin in staging.
+{% if 'runroot' in group_names %}
 ; Config for it lives in /etc/kojid/runroot.conf
 plugins = runroot
 
 ; We use the hub's plugin path since that's where
 ; the package installs the builder plugin.
 pluginpath = /usr/lib/koji-hub-plugins
+{% endif %}