lib/repo-pull: Use resolve() instead of list() in fetch_ref_contents()
lib/repo-pull: Use resolve() instead of list() in fetch_ref_contents()

This is more efficient in the non-collection case; in the collection
case, the implementation of ostree_repo_resolve_collection_ref() needs
to be rewritten to improve efficiency.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #1182
Approved by: cgwalters

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree