SPARK-4507: PR merge script should support closing multiple JIRA tickets

[hase1031]

This will fix SPARK-4507.

For pull requests that reference multiple JIRAs in their titles, it would be helpful if the PR merge script offered to close all of them.

[AmplabJenkins]

Can one of the admins verify this patch?

[liuchang0812]

This patch isn't very clear for reviewing, you moved a lot of codes. 👍

[hase1031]

I'll try not to move codes more than necessary

[aarondav]

does this change the behavior when there are no JIRAs of the correct form in the title, such that we now won't prompt the user?

[hase1031]

I fixed it.

[pwendell]

Jenkins, test this please.

[SparkQA]

Test build #23951 has started for PR 3428 at commit bf6d64b.

• This patch merges cleanly.

[pwendell]

LGTM pending tests.

[SparkQA]

Test build #23951 has finished for PR 3428 at commit bf6d64b.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/23951/
Test PASSed.

[pwendell]

Thanks @aarondav for the review and @hase1031 for this patch. I'll pull it in now.