Disambiguate logs in delete_allocation_for_instance

Two different error conditions in
SchedulerReportClient.delete_allocation_for_instance printed the same
warning log, which could be confusing. Reword one of them to
disambiguate.

Change-Id: Id1c5493a7270f2d0594e918df8704f671416a221

Author: Eric Fried

nova/scheduler/client/report.py

@@ -1998,7 +1998,8 @@ def delete_allocation_for_instance(self, context, uuid,
             # at the moment there is no way placement returns a failure so we
             # could even delete this code
             LOG.warning('Unable to delete allocation for %(consumer_type)s '
-                        '%(uuid)s: (%(code)i %(text)s)',
+                        '%(uuid)s. Got %(code)i while retrieving existing '
+                        'allocations: (%(text)s)',
                         {'consumer_type': consumer_type,
                          'uuid': uuid,
                          'code': r.status_code,