Fix/some fix

[fengjiachun]

Motivation:

1. fix maybe a recycle memory leak bug
2. add read-index timeout scanner to fail faster.

Modification:

Result:

[killme2008]

其他没啥问题，建议这次合并后近期发个版本

[fengjiachun]

增加一个内部类 TimeScanner 用于 create timer，做到 lazy 初始化，避免用户在关闭超时功能的情况下构建了不需要的 timer

[fengjiachun]

其他没啥问题，建议这次合并后近期发个版本

预计本周内会发一个版本

[yuyang0423]

hi all, I got many times of this read-index timeout issue, Does this familiar with you guys?

2020-08-05 12:54:49.563 [rheakv-read-index-callback #1] WARN  RaftRawKVStore:83 - Fail to [get] with 'ReadIndex': Status[ETIMEDOUT<1010>: read-index request timeout], try to applying to the state machine.
2020-08-05 12:54:49.573 [JRaft-FSMCaller-Disruptor-0] ERROR RocksRawKVStore:255 - Fail to [GET], key: [2F66656465726174696F6E2F6E6F6465], java.lang.IllegalStateException: Should not send rpc response repeatedly!
    at com.alipay.remoting.rpc.protocol.RpcAsyncContext.sendResponse(RpcAsyncContext.java:65)
    at com.alipay.sofa.jraft.rpc.impl.BoltRpcServer$2$1.sendResponse(BoltRpcServer.java:100)
    at com.alipay.sofa.jraft.rhea.RequestProcessClosure.run(RequestProcessClosure.java:64)
    at com.alipay.sofa.jraft.rhea.RequestProcessClosure.sendResponse(RequestProcessClosure.java:56)
    at com.alipay.sofa.jraft.rhea.DefaultRegionKVService$10.run(DefaultRegionKVService.java:383)
    at com.alipay.sofa.jraft.rhea.storage.MetricsKVClosureAdapter.run(MetricsKVClosureAdapter.java:93)
    at com.alipay.sofa.jraft.rhea.storage.KVClosureAdapter.run(KVClosureAdapter.java:72)
    at com.alipay.sofa.jraft.rhea.storage.BaseRawKVStore.setSuccess(BaseRawKVStore.java:179)
    at com.alipay.sofa.jraft.rhea.storage.RocksRawKVStore.get(RocksRawKVStore.java:253)
    at com.alipay.sofa.jraft.rhea.storage.BaseRawKVStore.get(BaseRawKVStore.java:42)
    at com.alipay.sofa.jraft.rhea.storage.BatchRawKVStore.batchGet(BatchRawKVStore.java:111)
    at com.alipay.sofa.jraft.rhea.storage.KVStoreStateMachine.batchApply(KVStoreStateMachine.java:189)
    at com.alipay.sofa.jraft.rhea.storage.KVStoreStateMachine.batchApplyAndRecycle(KVStoreStateMachine.java:148)
    at com.alipay.sofa.jraft.rhea.storage.KVStoreStateMachine.onApply(KVStoreStateMachine.java:117)
    at com.alipay.sofa.jraft.core.FSMCallerImpl.doApplyTasks(FSMCallerImpl.java:539)
    at com.alipay.sofa.jraft.core.FSMCallerImpl.doCommitted(FSMCallerImpl.java:508)
    at com.alipay.sofa.jraft.core.FSMCallerImpl.runApplyTask(FSMCallerImpl.java:440)
    at com.alipay.sofa.jraft.core.FSMCallerImpl.access$100(FSMCallerImpl.java:73)
    at com.alipay.sofa.jraft.core.FSMCallerImpl$ApplyTaskHandler.onEvent(FSMCallerImpl.java:148)
    at com.alipay.sofa.jraft.core.FSMCallerImpl$ApplyTaskHandler.onEvent(FSMCallerImpl.java:142)
    at com.lmax.disruptor.BatchEventProcessor.run(BatchEventProcessor.java:137)
    at java.lang.Thread.run(Thread.java:745)