ACU: fix bug where empty blocks were pushed to feed

This wasn't causing any trouble other than lots of log messages in
influxpublisher.

socs/agents/acu/agent.py

@@ -640,7 +640,9 @@ def monitor(self, session, params):
                 del new_influx_blocks[k]
 
             for block in new_influx_blocks.values():
-                self.agent.publish_to_feed('acu_status_influx', block)
+                # Check that we have data (commands and corotator often don't)
+                if len(block['data']) > 0:
+                    self.agent.publish_to_feed('acu_status_influx', block)
             influx_blocks.update(new_influx_blocks)
 
             # Assemble data for aggregator ...