summarizer: better handling of local yaml files
    
    When reading a packager-provided yaml module file, some optional
    information like module name, module stream or module defaults can be
    missing. These are usually filled out by the module build service from
    the module's git repo. So to correctly handle local yamls, we cannot use
    the same modulemd_index_from_file call for both local and repo yamls.
    
    See https://github.com/fedora-modularity/libmodulemd/issues/125
    
    Signed-off-by: Rafael dos Santos <rdossant@redhat.com>