Refactor directory_get_from_dirserver to use request API.

  if (rs) {

    const dir_indirection_t indirection =

      get_via_tor ? DIRIND_ANONYMOUS : DIRIND_ONEHOP;

    directory_initiate_command_routerstatus(rs, dir_purpose,

                                            router_purpose,

                                            indirection,

                                            resource, NULL, 0,

                                            if_modified_since,

                                            guard_state);

    directory_request_t *req = directory_request_new(dir_purpose);

    directory_request_set_routerstatus(req, rs);

    directory_request_set_router_purpose(req, router_purpose);

    directory_request_set_indirection(req, indirection);

    directory_request_set_resource(req, resource);

    directory_request_set_if_modified_since(req, if_modified_since);

    if (guard_state)

      directory_request_set_guard_state(req, guard_state);

    directory_initiate_request(req);

    directory_request_free(req);

  } else {

    log_notice(LD_DIR,

               "While fetching directory info, "