invalid value for dcp_backlog

1. I create 3 buckets - src_bucket, dst_bucket and metadata. 

2. Create eventing function

3. Add a document to src bucket. Check if the document get copied to dst_bucket.

4. Delete src_bucket and re-create it.

5. add a doc in src_bucket and check the stats via -

curl -u Administrator:password http://172.23.109.225:8096/api/v1/stats 

[{"event_processing_stats":{"DCP_DELETION":1,"DCP_MUTATION":2,"DCP_SNAPSHOT":3,"DCP_STREAMREQ":1024},"events_remaining":{"dcp_backlog":0},"execution_stats":{"agg_queue_size":0,"doc_timer_create_failure":0,"on_delete_failure":1,"on_delete_success":0,"on_update_failure":0,"on_update_success":2},"failure_stats":{"bucket_op_exception_count":1,"checkpoint_failure_count":0,"n1ql_op_exception_count":0,"timeout_count":0},"function_name":"test_event","lcb_exception_stats":{"13":1},"planner_stats":[\{"host_name":"172.23.109.225:8096","start_vb":0,"vb_count":1024}],"vb_distribution_stats":{"172.23.109.225:8096":{"worker_test_event_0":"[0-341]","worker_test_event_1":"[342-682]","worker_test_event_2":"[683-1023]"}},"worker_pids":{"worker_test_event_0":6260,"worker_test_event_1":6265,"worker_test_event_2":6259}}]