Store owner_id on Stack so updates maintain it

Instead of passing owner to the store() method of parser.Stack,
it is now maintained as an attribute of the Stack instance,
and store() will use that saved attribute when saving.

This fixes the problem of losing the owner_id on updates to
a stack.

Fixes bug 1212013

Change-Id: I1e3b7832291ca0f5cda24c1995ab782824e48943
Merge "Store owner_id on Stack so updates maintain it"