make the txid continuous and bug fixed

[mycFelix]

hello, i'm Felix.

When we used Trident API and set Config.TOPOLOGY_MAX_SPOUT_PENDING greater than 1, assuming 100, we found the txid was incontinuous.

That phenomenon has two effects:

• When using TransactionalTridentKafkaSpout class, we got different txid and continuance offset value but the process speed would be slow, because some unnecessary loops in function MasterBatchCoordinator.sync(). And the greater Config.TOPOLOGY_MAX_SPOUT_PENDING, the slower speed.
  we printed some logs here:

Config.TOPOLOGY_MAX_SPOUT_PENDING=100
Config.TOPOLOGY_TRIDENT_BATCH_EMIT_INTERVAL_MILLIS=50
14:05:00.337 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:135,offset:2546,nextOffset:2565]
14:05:00.483 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:136,offset:2565,nextOffset:2584]
14:05:00.495 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:197,offset:2584,nextOffset:2603]
14:05:03.550 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:198,offset:2603,nextOffset:2622]
14:05:03.593 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:199,offset:2622,nextOffset:2641]
please NOTICE the timestamp from id 136 to 198 and offset.
Config.TOPOLOGY_MAX_SPOUT_PENDING=1000
Config.TOPOLOGY_TRIDENT_BATCH_EMIT_INTERVAL_MILLIS=50
11:35:36.265 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:232,offset:228,nextOffset:247]
11:35:36.305 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:233,offset:247,nextOffset:266]
11:35:36.343 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:446,offset:266,nextOffset:285]
11:35:41.345 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:1266,offset:285,nextOffset:304]
11:35:47.063 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:1330,offset:304,nextOffset:323]
11:35:56.221 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:1447,offset:323,nextOffset:342]
please notice every log's timestamp,txid and offset.

• When using OpaqueTridentKafkaSpout class, we found that the different txid got same offset value which lead that we got repeated value from kafka.
  we printed some logs here:

11:10:13.516 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:96,offset:1805,nextOffset:1824]
11:10:13.567 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:142,offset:1824,nextOffset:1843]
11:10:13.619 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:97,offset:1824,nextOffset:1843]
11:10:13.670 [Thread-15-spout0] ERROR s.kafka.trident.TridentKafkaEmitter - emit:[id:98,offset:1843,nextOffset:1862]
please NOTICE that id 142 and 97 got same kafka offset.

We thought the txid's distribution algorithm needs to be with the continuous principle in MasterBatchCoordinator class. ONLY when the time windows and other condition is ready, the txid could be added.