KYLIN-5538 fix thread leak

[liuzhao-lz]

Proposed changes

发现kylin4在build job后都会重新new Broadcaster，Broadcaster构造器中会创建一个线程池然后执行任务不停的take广播事件。这个会导致每次构建完job都会创建线程，同时线程也会阻塞在takeFirst处，时间推移服务会不可用。

Branch to commit

• Branch kylin3 for v2.x to v3.x
• Branch kylin4 for v4.x
• Branch kylin5 for v5.x

Types of changes

What types of changes does your code introduce to Kylin?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I have created an issue on Kylin's jira, and have described the bug/feature there in detail
• Commit messages in my PR start with the related jira ID, like "KYLIN-0000 Make Kylin project open-source"
• Compiling and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged

Further comments

If this is a relatively large or complex change, kick off the discussion at user@kylin.apache.org or dev@kylin.apache.org by explaining why you chose the solution you did and what alternatives you considered, etc...