parser.Stack accepts tenant_id as a param

Previously, parser.Stack was exclusively using the tenant_id from
the request context.  However, when we load an existing stack, it makes
sense to use the existing tenant information from the stack in the
db (the source of truth) rather than the tenant info from the request
context.

Change-Id: I0906cf067e7a3c3fb29a427b6fb7b49f2ee859a4
Closes-Bug: 1246123