Convergence: engine restart doesn't start provisioning of the in progress stacks

[Anant Patil]

On of the prime goals in convergence was that engine restarts/system reboots shouldn't affect the in progress stack. The stacks that were in progress should start from where they were left. The design of convergence makes sure that enough data is there in DB to re-provision the stack from where it was left.
This approach contradicts the approach taken in legacy engine, where the stack and resources are marked as failed and user intervention is required to re-provision the stack.