Add "backup" column to stack table

Adds a backup boolean field to the stack record, defaulted to False,
with a migration which sets it to True for existing backup stacks,
which are named stackname* (which is an invalid name for any non-
backup stack).  Also adds the related column to the DB model and the
Stack object, so when we store a backup stack the flag will be set.

blueprint: list-nested
Change-Id: I737596a7248e8dd0c18a3f444f3b39a2b2e966c8
engine service add owner_id to create_stack

Adds owner_id as an optional argument to the top-level interface for
handling stack-creates, so it will be possible to create a nested stack
via an RPC call between engines.

Change-Id: I319e0d906d6ad54da6ce782a8a9dd9704f40e225
blueprint: decouple-nested
rpc client test remove rpcapi logic

Remove the test logic which allows overriding the rpcapi, since this
is not used anywhere.  Instead make the rpcapi a test class attribute
so it can be more easily used inside tests.

Change-Id: I21902f46919674093945c84fffda5a8e276f76b5
Merge "Add "backup" column to stack table"
Merge "rpc client test remove rpcapi logic"