Helper function, writes minion id to a cache file.

def _cache_id(minion_id, cache_file):
    '''
    Helper function, writes minion id to a cache file.
    '''
    path = os.path.dirname(cache_file)
    try:
        if not os.path.isdir(path):
            os.makedirs(path)
    except OSError as exc:
        # Handle race condition where dir is created after os.path.isdir check
        if os.path.isdir(path):
            pass
        else:
            log.error('Failed to create dirs to minion_id file: %s', exc)

    try:
        with salt.utils.files.fopen(cache_file, 'w') as idf:
            idf.write(minion_id)
    except (IOError, OSError) as exc:
        log.error('Could not cache minion ID: %s', exc)