Recent LDAP refactoring replaced entry_attrs regular dict with
normalized keys (i.e. lowercase) with LDAPEntry instance which keys
may not be normalized. This broke CND command output when
--structured and --all options were used.
Force lowercase normalization of the LDAPEntry keys in DNS plugin
structured format postprocessing. Also add a missing test for
DNS record structured output.
https://fedorahosted.org/freeipa/ticket/3526