Refined fix for validating image on rebuild

This aims to fix the issue described in bug 1664931 where a rebuild
fails to validate the existing host with the scheduler when a new
image is provided. The previous attempt to do this could cause rebuilds
to fail unnecessarily because we ran _all_ of the filters during a
rebuild, which could cause usage/resource filters to prevent an otherwise
valid rebuild from succeeding.

This aims to classify filters as useful for rebuild or not, and only apply
the former during a rebuild scheduler check. We do this by using an internal
scheduler hint, indicating our intent. This should (a) filter out
all hosts other than the one we're running on and (b) be detectable by
the filtering infrastructure as an internally-generated scheduling request
in order to trigger the correct filtering behavior.

Closes-Bug: #1664931
Change-Id: I1a46ef1503be2febcd20f4594f44344d05525446

nova/scheduler/filters/aggregate_image_properties_isolation.py

@@ -32,6 +32,8 @@ class AggregateImagePropertiesIsolation(filters.BaseHostFilter):
     # Aggregate data and instance type does not change within a request
     run_filter_once_per_request = True
 
+    RUN_ON_REBUILD = True
+
     def host_passes(self, host_state, spec_obj):
         """Checks a host in an aggregate that metadata key/value match
         with image properties.

nova/scheduler/filters/aggregate_instance_extra_specs.py

@@ -33,6 +33,8 @@ class AggregateInstanceExtraSpecsFilter(filters.BaseHostFilter):
     # Aggregate data and instance type does not change within a request
     run_filter_once_per_request = True
 
+    RUN_ON_REBUILD = False
+
     def host_passes(self, host_state, spec_obj):
         """Return a list of hosts that can create instance_type
 

nova/scheduler/filters/aggregate_multitenancy_isolation.py

@@ -28,6 +28,8 @@ class AggregateMultiTenancyIsolation(filters.BaseHostFilter):
     # Aggregate data and tenant do not change within a request
     run_filter_once_per_request = True
 
+    RUN_ON_REBUILD = False
+
     def host_passes(self, host_state, spec_obj):
         """If a host is in an aggregate that has the metadata key
         "filter_tenant_id" it can only create instances from that tenant(s).