store_json: Fix parent/child detection.

Rewinding the formatter state has to happen any time we see a parent object of
the current object. This happens every time the current context isn't HOST
(hosts don't have any parents) or the new object is an ATTRIBUTE (which are
always children of whatever other object type).

This broke in 3603db13105aefac4d6ceb356bcfd118a92fa654.