Compute instance clean up daemon process

If the Compute server goes down while an instance is being created, the instance remains in 'building' state. Even after the Compute server comes up again, the instance remains in the same state.
We need to add a daemon process in Compute, that checks the instance status, updates the status to 'error' (if it has been in 'building' status for long). This process should also check and release any resources allocated to the instance (if any).