Add custom hop hints and fix self payment #1901

Job	Run time
e2e test for 3-nodes-transfer --env test	4m 20s
e2e test for invoice-ops --env test	4m 20s
e2e test for open-use-close-a-channel --env test	4m 46s
e2e test for udt --env test	4m 18s
e2e test for reestablish --env test	4m 13s
e2e test for cross-chain-hub --env test	4m 16s
e2e test for router-pay --env test	5m 7s
e2e test for udt-router-pay --env test	4m 28s
e2e test for watchtower --env test	5m 54s
e2e test for udt --env xudt-test	4m 36s
e2e test for 3-nodes-transfer --env test --env-var HASH_ALGORITHM=sha256	4m 17s
	50m 35s

Provide feedback