fix deadlock

[aloyszhang]

fix #181
This pull request fix the deadlock in kop.

[jiazhai]

@aloyszhang Thanks for the work.
ci failed at mvn spotbugs:check

[ERROR] io.streamnative.pulsar.handlers.kop.utils.timer.TimerTask.getTimerTaskEntry() is unsynchronized, io.streamnative.pulsar.handlers.kop.utils.timer.TimerTask.setTimerTaskEntry(TimerTaskList$TimerTaskEntry) is synchronized [io.streamnative.pulsar.handlers.kop.utils.timer.TimerTask] At TimerTask.java:[line 50] UG_SYNC_SET_UNSYNC_GET

[aloyszhang]

@jiazhai
It's caused by we remove synchronized only from TimerTask#getTimerTaskEntry but Spotbug check synchronized for both getter and setter.
Now fixed by moving synchronized from TimerTask#setTimerTaskEntry to inside method and replace with synchronized (this)
But CI stilled failed for ThreadTimeoutException in KafkaIntegrationTest, can you help on this problem?