Re-implemented lookup_result_t to use lazy initialization

Hostname, port, addr and path take values only if it is needed
Example:
  lookup_result_t lr = proxy->lookup(key);
  uint16_t port = lr.port();
Only port will be resolved in this case

async_write_result_t was implemented as wrapper to ioremap::elliptics::async_write_result to convert lookup_result_entry to lookup_result_t

now lookup-list updates with last iteration in chunk-write so fix_size method is no longer needed