load manifest from file

def _load_manifest_from_file(manifest, path):
    """ load manifest from file """
    path = os.path.abspath(os.path.expanduser(path))
    if not os.path.exists(path):
        raise ManifestException("Manifest does not exist at {0}!".format(path))
    manifest.read(path)
    if not manifest.has_option('config', 'source'):
        manifest.set('config', 'source', str(path))