BUG/MINOR: dns: check for duplicate nameserver id in a resolvers section was missing

Current resolvers section parsing function is permissive on nameserver
id and two nameservers may have the same id.
It's a shame, since we don't know for example, whose statistics belong
to which nameserver...

From now, configuration with duplicated nameserver id in a resolvers
section are considered as broken and returns a fatal error when parsing.
1 file changed