[attribute] Add "length" attribute to reset() tests

A "length" attribute is causing attr.reset() to fail
[attribute] Fix #1537. Assume state data is an object

Using Y.each() instead of Y.Object.each() failed when state data had a
"length" property
Merge branch 'attr-reset-length' into dev-master
Merge branch 'dev-master' into dev-3.x