[BUILD] Closing some stale/inappropriate PRs

[HyukjinKwon]

What changes were proposed in this pull request?

This PR proposes to close some stale PRs and ones suggested to be closed by committer(s) or obviously inappropriate PRs (e.g. branch to branch).

Closes #15689
Closes #14640
Closes #15917
Closes #16188
Closes #16206

How was this patch tested?

N/A

[HyukjinKwon]

cc @srowen Could you take a look and see if they are reasonable please?

[SparkQA]

Test build #69847 has started for PR 16207 at commit c51011c.

[rxin]

Merging in master.

[rxin]

For some reason I couldn't merge this one. I pushed a commit directly to master. Can you close this one now?

[HyukjinKwon]

Sure, thanks!

[HyukjinKwon]

BTW, I believe we should add --allow-empty when it is merged.

[srowen]

Yes I have to edit the merge script to git commit --allow-empty ... but I don't know that we should always set it. It could prompt or something but I was too lazy to implement that.

Anyway that sounds fine and I have my own list of PRs to close that I'll 'flush' with a commit soon too.

[rxin]

Yea i'd say in general that --allow-empty shouldn't be there.

[AmplabJenkins]

Test FAILed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/69847/
Test FAILed.