Fixes the reroute_compute decorator in the scheduler API so that it properly:
Fixes the reroute_compute decorator in the scheduler API so that it properly:

1) Raises InstanceNotFound when all zones return no instance
2) If an instance is found in a zone, ignore whether other zones may be down.  Return the instance
information, catching the novaclient exceptions from the other zones.
3) If a zone is down and no instances are found in other zones, raise a ZoneRequestError... as it's possible the instance exists in the downed zones.

citrix-openstack-build/oslo.versionedobjects,openstack/oslo.versionedobjects