Generates a list of salt://<formula>/defaults.(json|yaml) files
    and fetches them from the Salt master.

    Returns first defaults file as python dict.

def _load(formula):
    '''
    Generates a list of salt://<formula>/defaults.(json|yaml) files
    and fetches them from the Salt master.

    Returns first defaults file as python dict.
    '''

    # Compute possibilities
    _mk_client()
    paths = []
    for ext in ('yaml', 'json'):
        source_url = salt.utils.url.create(formula + '/defaults.' + ext)
        paths.append(source_url)
    # Fetch files from master
    defaults_files = __context__['cp.fileclient'].cache_files(paths)

    for file_ in defaults_files:
        if not file_:
            # Skip empty string returned by cp.fileclient.cache_files.
            continue

        suffix = file_.rsplit('.', 1)[-1]
        if suffix == 'yaml':
            loader = salt.utils.yaml.safe_load
        elif suffix == 'json':
            loader = salt.utils.json.load
        else:
            log.debug("Failed to determine loader for %r", file_)
            continue

        if os.path.exists(file_):
            log.debug("Reading defaults from %r", file_)
            with salt.utils.files.fopen(file_) as fhr:
                defaults = loader(fhr)
                log.debug("Read defaults %r", defaults)

            return defaults or {}