Use oslo db.migration script

Turn Heat's migration script into a simple wrapper around olso's.
The api is a bit different so for now keep ours inplace.
All that our script does is find the path to the migration_repo
and call the oslo code. No point having two implementations in the
same codebase.

Change-Id: I0aa3e10890f924d77268f4118dae53b446e193eb
Merge "Refactor Instance#_check_active"
Merge "Use oslo db.migration script"
Add filter and pagination to stack_get_all

This change prepares the ground for calls that are not tenant-scoped
to make use of the filter and paging capabilities.

Implements: blueprint management-api
Change-Id: I4862752999629666b46da20c2713edc950c5d52e
Unscoped List Stacks

This allows non tenant-scoped list of stacks for the management api
blueprint.  A user with a service_admin role will be able to make a call
to /tenant_id/stacks and get all the stacks, and not just the ones owned
by them, effectively bypassing the tenant scoping.

If the user is not an admin, only their stacks will be returned
(unchanged behavior).

The db_api is now the gate to scope stacks by tenant appropriately.
Users that do not pass the service_admin rule as defined by the policy
will have requests to the DB scoped by their tenant_id.

Implements: blueprint management-api
Change-Id: I973a7ad2726eb6d9c972d08abe15e241aa120ec3