Add unit test for last hop stopped #2043

Job	Run time
e2e test for 3-nodes-transfer --env test	4m 43s
e2e test for invoice-ops --env test	4m 8s
e2e test for open-use-close-a-channel --env test	4m 1s
e2e test for udt --env test	4m 41s
e2e test for reestablish --env test	4m 18s
e2e test for cross-chain-hub --env test	4m 17s
e2e test for router-pay --env test	5m 37s
e2e test for udt-router-pay --env test	4m 18s
e2e test for watchtower --env test	5m 50s
e2e test for udt --env xudt-test	4m 47s
e2e test for 3-nodes-transfer --env test --env-var HASH_ALGORITHM=sha256	4m 27s
	51m 7s

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