preconfigure chrony to use NTP servers from the respective
pools for SUSE and openSUSE (bsc#1156884, SLE-11424).
- Add chrony-pool-empty to still allow installing chrony without
preconfigured servers.
- Use iburst in the default pool statements to speed up initial
synchronisation (bsc#1172113).
OBS-URL: https://build.opensuse.org/package/show/network:time/chrony?expand=0&rev=85
