F #-: VR: Add auto DNS names + multiple fixes (#13)

Virtual Router:
* use TCP_CHECK for LVS TCP (fix)
* Do NOT stop iptables together with (SD)NAT4 (fix)
* Switch from "ip --json" to context vars (fix)
* Add local-zone DNS names
* Exclude VIPs from IP ranges (fix)
* Cosmetic improvements
* Use "via" instead of deprecated "gw"

Update SDNAT4, DHCP, DNS.