'Update the given metadata in the headers
:param headers: The headers dictionary to be updated
:type headers: ``dict``
:param meta_data: Metadata key value pairs
:type meta_data: ``dict``'

def _update_metadata(self, headers, meta_data):

    for (key, value) in list(meta_data.items()):
        key = ('x-ms-meta-%s' % key)
        headers[key] = value
