Create a daemon thread pool for etcd client & Add name format for ExecutorService

[zhongqishang]

What problem does this PR solve?

When my main thread is finished with all the tasks processed, this pool will prevent my program shutting down.
TiDBCatalogDemo.java

What is changed and how it works?

1. Create a daemon thread pool for etcd client
2. Add name format for ExecutorService

Check List

• Manual test (add detailed scripts or steps below)
  Test in local with version 3.0.1, thread stack :

"PDClient-tiflash-replica-pool-0@8667" daemon prio=5 tid=0x46 nid=NA waiting
  java.lang.Thread.State: WAITING
	  at sun.misc.Unsafe.park(Unsafe.java:-1)
	  at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
	  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
	  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
	  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
	  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
	  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
	  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	  at java.lang.Thread.run(Thread.java:748)
"PDClient-update-leader-pool-0@8666" daemon prio=5 tid=0x45 nid=NA waiting
  java.lang.Thread.State: WAITING
	  at sun.misc.Unsafe.park(Unsafe.java:-1)
	  at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
	  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
	  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
	  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
	  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
	  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
	  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	  at java.lang.Thread.run(Thread.java:748)
"etcd-conn-manager-pool-0@9096" daemon prio=5 tid=0x48 nid=NA waiting
  java.lang.Thread.State: WAITING
	  at sun.misc.Unsafe.park(Unsafe.java:-1)
	  at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
	  at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:460)
	  at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:362)
	  at java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:941)
	  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1073)
	  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
	  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	  at java.lang.Thread.run(Thread.java:748)

Related changes

• Need to cherry-pick to the release branch

[marsishandsome]

LGTM

[marsishandsome]

@birdstorm PTAL

[birdstorm]

LGTM, nice work!

[birdstorm]

/merge

[ti-srebot]

/run-all-tests

[ti-srebot]

cherry pick to release-3.1 in PR #168