option to not render all defaults into config file if not required

Hi,

Thanks for the cookbook. We are running chrony-3.1-2.el7.centos.x86_64 and are getting the following warnings in the journal:

chronyd[14075]: commandkey directive is no longer supported chronyd[14075]: generatecommandkey directive is no longer supported

It would be nice to have an option to exclude some default attributes that we do not require to be rendered into the config file, maybe by giving a specific value to the attribute.

plain chrony.conf on install I would like to be able to reproduce it like this :

server 0.centos.pool.ntp.org iburst server 1.centos.pool.ntp.org iburst server 2.centos.pool.ntp.org iburst server 3.centos.pool.ntp.org iburst driftfile /var/lib/chrony/drift makestep 1.0 3 rtcsync logdir /var/log/chrony

Many thanks,