pillar/device-steps.sh: fix global NTPSERVER var initialization

[rouming]

A few commits target the following:

1. On NTP servers restart NTPSERVER variable should be assigned, otherwise chrony will be reloaded with same values.
2. Handle absence of the DeviceNetworkStatus/global.json correctly and return default pool.
3. Make NTP servers sorted and uniq
4. Make error path of the dialUnixWithChronyd() cleaner by moving socket cleanup directly into the function.
5. Report DNS name of the NTP peer, so do the reverse lookup.