Alter stack_count_all_by_tenant to stack_count_all

Preparing the database for the unscoped list stacks, this removes
stack_count_all_by_tenant in favor of a single function that is tenant
aware.  This way, you can call stack_count_all(tenant_safe=False) and
count all stacks, regardless of the tenants.

tenant_safe defaults to True.

Co-Authored-By: Anderson Mesquita <andersonvom@gmail.com>
Implements: blueprint management-api (partial)
Change-Id: Ic44b884120290b6ceaf4936e015ef6661aaf6694
Merge "Alter stack_count_all_by_tenant to stack_count_all"