Add exception logging if flow creation fails

If the create_XYZ_flow fails in being created
its useful to log exactly what the error was in
detail (instead of trapping it and only raising
a generic error). The more detailed error shows
what the real problem was during the flows
construction (which usually is some larger
problem).

Change-Id: I9cd6b8e2c6298d8791ba3063be78f9b4c4a7c5d0

cinder/scheduler/manager.py

@@ -84,6 +84,7 @@ class SchedulerManager(manager.Manager):
                                                            snapshot_id,
                                                            image_id)
         except Exception:
+            LOG.exception(_("Failed to create scheduler manager volume flow"))
             raise exception.CinderException(
                 _("Failed to create scheduler manager volume flow"))
         flow_engine.run()