Currently the pid file is not deleted, and potentially may cause some problem after service is stopped. The fix remove the pid file after service stopped.

Author: Zhan Zhang <zhazhan@gmail.com>

Closes #4676 from zhzhan/spark-5889 and squashes the following commits:

eb01be1 [Zhan Zhang] solve review comments
b4c009e [Zhan Zhang] solve review comments
018110a [Zhan Zhang] spark-5889: remove pid file after stopping service
088d2a2 [Zhan Zhang] squash all commits
c1f1fa5 [Zhan Zhang] test