Fix publisher resource leak in librarian submit_document (#883)

Wrap pub.start()/pub.send() in try/finally to guarantee pub.stop() is
called on error. Remove unnecessary asyncio.sleep(1) kludge.

trustgraph-flow/trustgraph/librarian/service.py

@@ -418,13 +418,10 @@ class Processor(AsyncProcessor):
             self.pubsub, q, schema=schema
         )
 
+        try:
             await pub.start()
-
-        # FIXME: Time wait kludge?
-        await asyncio.sleep(1)
-
             await pub.send(None, doc)
-
+        finally:
             await pub.stop()
 
         logger.debug("Document submitted")