Fix bug in mongodb backend for dead letter queue

In the function{ClaimController:create} for mongodb backend, there
is an error when a message is inserted to the dead letter
queue.Because a mongodb collection(messages) is shared by
many queues, we need to delete first and then insert,
otherwise insert_one will cause the following error:
pymongo.errors.DuplicateKeyError: insertDocument :: caused by ::
11000 E11000 duplicate key error index: admin.test.$_id_  dup key:
{ : ObjectId('xxxxxxxxxxxxxxxxxxxxxx') }

Depends-On: I1ee88a8963e2bc80172710da5ab60313952495e4
Depends-On: I8c3642f3883ecc68853735636fc3a748b9c780b6
Closes-Bug: #1707814
Change-Id: If7824d135ecd6999716954e6fa4fa000434c4ed4

zaqar/tests/tempest_plugin/tests/v2/test_claims.py

@@ -13,6 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import time
+
 from six.moves.urllib import parse as urlparse
 from tempest import config
 from tempest.lib.common.utils import data_utils
@@ -108,6 +110,44 @@ class TestClaims(base.BaseV2MessagingTest):
         message_uri = urlparse.urlparse(claim_uri).path
         self.client.delete_messages(message_uri)
 
+    @decorators.idempotent_id('c1975970-66e7-11e7-a771-fa163e40e1ff')
+    def test_dead_letter_queue(self):
+        # Post Messages
+        QueueName = "QueueWithDLQ"
+        DLQ_name = "DLQ"
+        meta = {'ttl': 60, 'grace': 60}
+        # Set dead letter queeu metadata
+        op1 = {"op": "add",
+               "path": "/metadata/_max_claim_count", "value": 2}
+        op2 = {"op": "add",
+               "path": "/metadata/_dead_letter_queue", "value": DLQ_name}
+        op3 = {"op": "add",
+               "path": "/metadata/_dead_letter_queue_messages_ttl",
+               "value": 7799}
+        metadata = [op1, op2, op3]
+        self.client.create_queue(QueueName)
+        self.client.create_queue(DLQ_name)
+        self.set_queue_metadata(QueueName, metadata)
+        message_body = self.generate_message_body(repeat=1)
+        self.client.post_messages(queue_name=QueueName,
+                                  rbody=message_body)
+
+        for i in range(3):
+            resp, body = self.client.post_claims(
+                queue_name=QueueName,
+                rbody=meta)
+            if(i == 2):
+                self.assertEqual('204', resp['status'])
+            else:
+                self.assertEqual('201', resp['status'])
+                self.assertEqual(1, len(body["messages"]))
+                time.sleep(70)
+
+        resp, body = self.client.list_messages(DLQ_name)
+        self.assertEqual('200', resp['status'])
+        self.client.delete_queue(DLQ_name)
+        self.client.delete_queue(QueueName)
+
     @classmethod
     def resource_cleanup(cls):
         cls.delete_queue(cls.queue_name)