lib/pull: Avoid journaling 404s for optional content

Currently in Fedora we don't sign summaries, and every use of
`rpm-ostree` would emit to the journal an error when we failed
to fetch it.

Fix this by having `OSTREE_FETCHER_REQUEST_OPTIONAL_CONTENT` tell the fetcher
not to journal 404 errors. While fixing this, we had a mix of two booleans vs
the flags; fix things so we consistently use the flags in the fetcher and pull
code.

Closes: #1004
Approved by: mbarnes

src/libostree/ostree-metalink.c

@@ -431,10 +431,7 @@ try_one_url (OstreeMetalinkRequest *self,
   gssize n_bytes;
 
   if (!_ostree_fetcher_request_uri_to_membuf (self->metalink->fetcher,
-                                              uri,
-                                              FALSE,
-                                              FALSE,
-                                              &bytes,
+                                              uri, 0, &bytes,
                                               self->metalink->max_size,
                                               self->cancellable,
                                               error))
@@ -614,14 +611,9 @@ _ostree_metalink_request_sync (OstreeMetalink        *self,
   request.urls = g_ptr_array_new_with_free_func ((GDestroyNotify) _ostree_fetcher_uri_free);
   request.parser = g_markup_parse_context_new (&metalink_parser, G_MARKUP_PREFIX_ERROR_POSITION, &request, NULL);
 
-  if (!_ostree_fetcher_request_uri_to_membuf (self->fetcher,
-                                              self->uri,
-                                              FALSE,
-                                              FALSE,
-                                              &contents,
-                                              self->max_size,
-                                              cancellable,
-                                              error))
+  if (!_ostree_fetcher_request_uri_to_membuf (self->fetcher, self->uri, 0,
+                                              &contents, self->max_size,
+                                              cancellable, error))
     goto out;
 
   data = g_bytes_get_data (contents, &len);