heap-use-after-free risk caused by direct deconstruction in factory manager test.

[ShannonDing]

1. Please tell us about your environment:

• What is your OS?
  centos7.2
• What is your client version?
  2.0.1
• What is your RocketMQ version?
  4.6.0

3. Other information (e.g. detailed explanation, logs, related issues, suggestions on how to fix, etc):

• The ASAN Report
  [==========]Running 2 tests from 1 test case.
  [----------]Global test environment set-up.
  [----------]2 tests from MQClientManagerTest
  [ RUN ]MQClientManagerTest.getClientFactory
  =================================================================
  ==124436==ERROR: AddressSanitizer: heap-use-after-free on address 0x6110000096f8 at pc
  0x7efe51699cba bp 0x7efe4bdfac20 sp 0x7efe4bdfac18
  WRITE of size 8 at 0x6110000096f8 thread T4 (RemotingAsioT)
  [ OK ] MQClientManagerTest.getClientFactory (14 ms)
  [ RUN ] MQClientManagerTest.removeClientFactory
  [ OK ] MQClientManagerTest.removeClientFactory (0 ms)
  [----------] 2 tests from MQClientManagerTest (14 ms total)
  [----------] Global test environment tear-down
  [==========] 2 tests from 1 test case ran. (14 ms total)
  [ PASSED ] 2 tests.