Replace stack_get_all_by_tenant with stack_get_all

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

tenant_safe defaults to True.

Implements: blueprint management-api (partial)
Change-Id: Ifdcfc44a3483a089ae803cfd044151262957674a
Merge "Replace stack_get_all_by_tenant with stack_get_all"