[SPARK-3233] Executor never stop its SparnEnv, BlockManager, ConnectionManager etc.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #2138 from sarutak/SPARK-3233 and squashes the following commits:

c0205b7 [Kousuke Saruta] Merge branch 'SPARK-3233' of github.com:sarutak/spark into SPARK-3233
064679d [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-3233
d3005fd [Kousuke Saruta] Modified Class definition format of BlockManagerMaster
039b747 [Kousuke Saruta] Modified style
889e2d1 [Kousuke Saruta] Modified BlockManagerMaster to be able to be past isDriver flag
4da8535 [Kousuke Saruta] Modified BlockManagerMaster#stop to send StopBlockManagerMaster message when sender is Driver
6518c3a [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-3233
d5ab19a [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-3233
6bce25c [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-3233
6058a58 [Kousuke Saruta] Modified Executor not to invoke SparkEnv#stop in local mode
e5ad9d3 [Kousuke Saruta] Modified Executor to stop SparnEnv at the end of itself