Correct multi-line neutron attribute detection

The way that arrays were built-up for multi-line items caused the arrays
to become more tested with each element, making structures like
[[[a, b], c], d]

This corrects the behavior

Change-Id: I045abdfefd6f2cc85d0d9c70d3375fdce302f05d
(cherry picked from commit 0c82dfd436ff987aac70f5fc8440874f89b1155e)
Merge "Correct multi-line neutron attribute detection" into stable/havana