dns: move code called on client to the module level
    
    Move DNSRecord and dnsrecord code called on client to module-level
    functions.
    
    This will make it possible to move the code to ipaclient without the
    DNSRecord and dnsrecord class bits.
    
    https://fedorahosted.org/freeipa/ticket/4739
    
    Reviewed-By: David Kupka <dkupka@redhat.com>