[SPARK-28616][INFRA] Improve merge-spark-pr script to warn WIP PRs and strip trailing dots

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR aims to improve the merge-spark-pr script in the following two ways.

1. [WIP] is useful when we show that a PR is not ready for merge. Apache Spark allows merging WIP PRs. However, sometime, we accidentally forgot to clean up the title for the completed PRs. We had better warn once more during merging stage and get a confirmation from the committers.
2. We have two kinds of PR titles in terms of the ending period. This PR aims to remove the trailing dot since the shorter is the better in the commit title. Also, the PR titles without the trailing dot is dominant in the Apache Spark commit logs.

$ git log --oneline | grep '[.]$' | wc -l
    4090
$ git log --oneline | grep '[^.]$' | wc -l
   20747

How was this patch tested?

Manual.

$ dev/merge_spark_pr.py
git rev-parse --abbrev-ref HEAD
Which pull request would you like to merge? (e.g. 34): 25157

The PR title has `[WIP]`:
[WIP][SPARK-28396][SQL] Add PathCatalog for data source V2
Continue? (y/n):

$ dev/merge_spark_pr.py
git rev-parse --abbrev-ref HEAD
Which pull request would you like to merge? (e.g. 34): 25304
I've re-written the title as follows to match the standard format:
Original: [SPARK-28570][CORE][SHUFFLE] Make UnsafeShuffleWriter use the new API.
Modified: [SPARK-28570][CORE][SHUFFLE] Make UnsafeShuffleWriter use the new API
Would you like to use the modified title? (y/n):

[SparkQA]

Test build #108637 has finished for PR 25356 at commit 0e3c1a2.

• This patch fails SparkR unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

retest this please

[dongjoon-hyun]

All test passed and the CRAN check failed because they seems to start to enforce R 3.4 and the above.

* checking CRAN incoming feasibility ...Error in readRDS(con) : 
  ReadItem: unknown type 238, perhaps written by later version of R
Execution halted
During startup - Warning message:
In .First() :
  Support for R prior to version 3.4 is deprecated since Spark 3.0.0
Loading required package: methods

I'll merge this PR since this is not related to the Spark code.

[dongjoon-hyun]

Thank you always for review and approval, @HyukjinKwon !
Merged to master.

[dongjoon-hyun]

Oops. I didn't read your retest comment. Sorry for missing that~

[HyukjinKwon]

I think that's fine.

[AmplabJenkins]

Test FAILed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/108640/
Test FAILed.

[dongjoon-hyun]

I'll file a JIRA for CRAN failure since we need to upgrade R in Jenkins.

[HyukjinKwon]

Thanks.

* checking CRAN incoming feasibility ...Error in readRDS(con) : 
  ReadItem: unknown type 238, perhaps written by later version of R

This error seems to be newer one. cc @viirya FYI.

[dongjoon-hyun]

Ya. I'm checking the other commits and found that #24560 passed 4 hours ago without this problem. Maybe, it might be a transient issue. I'll keep monitoring~

[viirya]

• checking CRAN incoming feasibility ...Error in readRDS(con) :

Looks different to previous CRAN error. Was it happened again?

[HyukjinKwon]

Yes, seems so - #25363 (comment)

[HyukjinKwon]

looks intermittent though ..

[dongjoon-hyun]

I'll backport this to branch-2.4 because I noticed that branch-2.4 script is also used sometime.