Stack and its nested stacks should be in *_COMPLETE state for
it to be migrated. Also, we should not allow migration of a
nested stack.
This also changes stack_get_all_by_owner_id() to not select the
backup stacks. This seems to be used only in convergence code
path and migrate_convergence_1().
Change-Id: Icd54465d0c593557a12d853ddee4ee8ce6483499
Closes-Bug: #1767962
Story: #1767962
Task: #17363