yum-updatesd: switch configuration to a template

This allows the emit method to be configurable. There are a couple
possibilities, but this change only adds "email" and "dbus".
Rather than adding these very specific settings I'm add a single one that le's you customize the template to use, something like:
updatesd_template = 'yum/yum-updatesd.erb',
if you want to customize, you provide a custom one