Migrate OnboardingController to SSA status updates

Replace PatchHypervisorStatusWithRetry with Status().Apply(). The Nova
ID lookup is inlined into Reconcile and combined with the initial
condition in a single apply, avoiding two applies from the same field
manager in one reconcile cycle which would cause SSA to prune the IDs.
HypervisorID and ServiceID are included in every subsequent apply to
retain ownership.

Author: fwiesel