libostree: Add ostree_repo_pull_with_options()

We potentially need a lot of argument types for pull.  Rather than
have a C function with tons of arguments, let's use a GVariant a{sv}
as a handy extensible (and immutable) bag of properties.

This is prepratory work for adding an option to pull to traverse
history.

https://bugzilla.gnome.org/show_bug.cgi?id=737844

src/libostree/ostree-repo.h

@@ -560,6 +560,13 @@ ostree_repo_pull_one_dir (OstreeRepo               *self,
                           GCancellable             *cancellable,
                           GError                  **error);
 
+gboolean ostree_repo_pull_with_options (OstreeRepo             *self,
+                                        const char             *remote_name,
+                                        GVariant               *options,
+                                        OstreeAsyncProgress    *progress,
+                                        GCancellable           *cancellable,
+                                        GError                **error);
+
 gboolean ostree_repo_sign_commit (OstreeRepo     *self,
                                   const gchar    *commit_checksum,
                                   const gchar    *key_id,