network_info cache should be cleared before being rescheduled

If an instance fails to boot due to a non-networking error the instance
then gets rescheduled and launched on another compute node. In these cases
deallocate_for_instance() is called which deletes the network ports
allocated though the info_cache for the instance is never cleared. This patch
adds a call to update_instance_cache_with_nw_info() which causes the cache
to get cleared out. Note: the cache is only cleared if the instance hasn't
been marked for deletion. This is due to how instance_info_cache_update()
is implemented.

Change-Id: If967884c9a6276f5949a7a04b597cedcce12ba09
Closes-bug: #1285158

nova/network/neutronv2/api.py

@@ -416,6 +416,13 @@ class API(base.Base):
                         LOG.exception(_("Failed to delete neutron port %s"),
                                       port)
 
+        # NOTE(arosen): This clears out the network_cache only if the instance
+        # hasn't already been deleted. This is needed when an instance fails to
+        # launch and is rescheduled onto another compute node. If the instance
+        # has already been deleted this call does nothing.
+        update_instance_info_cache(self, context, instance,
+                                   network_model.NetworkInfo([]))
+
     def allocate_port_for_instance(self, context, instance, port_id,
                                    network_id=None, requested_ip=None):
         """Allocate a port for the instance."""

nova/tests/network/test_neutronv2.py

@@ -960,6 +960,7 @@ class TestNeutronv2(TestNeutronv2Base):
                           self.instance, requested_networks=requested_networks)
 
     def _deallocate_for_instance(self, number):
+        api = neutronapi.API()
         port_data = number == 1 and self.port_data1 or self.port_data2
         self.moxed_client.list_ports(
             device_id=self.instance['uuid']).AndReturn(
@@ -967,6 +968,10 @@ class TestNeutronv2(TestNeutronv2Base):
         for port in reversed(port_data):
             self.moxed_client.delete_port(port['id'])
 
+        self.mox.StubOutWithMock(api.db, 'instance_info_cache_update')
+        api.db.instance_info_cache_update(self.context,
+                                          self.instance['uuid'],
+                                          {'network_info': '[]'})
         self.mox.ReplayAll()
 
         api = neutronapi.API()