Release all taken tasks on start

If some tasks have been taken and don't released before shutdown
of the tarantool instance (for example: tarantool instance has been killed)
such task go to 'hung' state (noone can take the task now).
So, we must release all taken tasks on start of the queue module.

Fixes #66

Author: LeonidVas

queue/abstract.lua

@@ -511,7 +511,20 @@ function method.start()
         })
     end
 
-    _queue:pairs():each(recreate_tube)
+    for _, tube_tuple in _queue:pairs() do
+        local space_name = tube_tuple[3]
+        tube = recreate_tube(tube_tuple)
+        local space = box.space[space_name]
+        for _, task_tuple in space:pairs() do
+            -- Release all taken tasks on start
+            -- See https://github.com/tarantool/queue/issues/66
+            -- for more information
+            local tid, task_state = task_tuple[1], task_tuple[2]
+            if task_state == state.TAKEN then
+                tube.raw:release(tid)
+            end
+        end
+    end
 
     session.on_disconnect(queue._on_consumer_disconnect)
     return queue