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-fetcher-util.h

@@ -29,8 +29,7 @@ G_BEGIN_DECLS
 gboolean _ostree_fetcher_mirrored_request_to_membuf (OstreeFetcher *fetcher,
                                                      GPtrArray     *mirrorlist,
                                                      const char    *filename,
-                                                     gboolean       add_nul,
-                                                     gboolean       allow_noent,
+                                                     OstreeFetcherRequestFlags flags,
                                                      GBytes         **out_contents,
                                                      guint64        max_size,
                                                      GCancellable   *cancellable,
@@ -38,8 +37,7 @@ gboolean _ostree_fetcher_mirrored_request_to_membuf (OstreeFetcher *fetcher,
 
 gboolean _ostree_fetcher_request_uri_to_membuf (OstreeFetcher *fetcher,
                                                 OstreeFetcherURI *uri,
-                                                gboolean       add_nul,
-                                                gboolean       allow_noent,
+                                                OstreeFetcherRequestFlags flags,
                                                 GBytes         **out_contents,
                                                 guint64        max_size,
                                                 GCancellable   *cancellable,