Improvements to checkstyle-tester

[nrmancuso]

From discussion at checkstyle/checkstyle#9121 (comment):

#530 - forgo tests. Looking at https://github.com/checkstyle/checkstyle/blob/master/.ci/no-exception-test.sh#L26-L27, it doesn't look like CI cares if HTML is created or not. It just requires maven to fail the build if it fails. Launch will eventually be removed too.
#524 and #527 - finish PR for new github repos.
#523 - first part of merging launch into diff. lets make this easy and just do copy/paste of what we can. ¿Maybe look into creating groovy tests?
#529 - Complete merging.
#367 - start some removals.
#273 - complete removals.

I see it as beneficial if we could make it show how the groovy scripts will behave with your new changes... Can you recommend the best way to do this?

https://groovy-lang.org/testing.html
Testing is going to be new for groovy. This also brings up a thought brought up before. Should we keep this as groovy or is it becoming so complex we should switch it to a Java project.

This issue is simply an umbrella to maintain the order of issues to address, since the original issue where this was discussed (checkstyle/checkstyle#9121 (comment)) will be closed.

[nrmancuso]

Minor addition, Sevntu also uses launch.groovy . See https://github.com/sevntu-checkstyle/sevntu.checkstyle/blob/master/sevntu-checks/.ci/wercker.sh#L35 . I am making updates to existing issues as I see/remember things we need to be mindful of in this revamp.

Originally posted by @rnveach in checkstyle/checkstyle#9121 (comment)

[rnveach]

@nmancus1 Feel free to start when you are ready.

[rnveach]

#524 and #527 - finish PR for new github repos.

This is optional for the improvements and can be skipped since there is an issue in merging it.

[nrmancuso]

@rnveach if you agree with comments at #523 (comment), then I can proceed with #529 this week. I will plan on adding groovy tests in #529 in this case.

[nrmancuso]

Update: I am currently working on #529. Some thoughts to leave here:

Regarding #273:
I plan to use @rnveach's scripts located at https://github.com/rnveach/contribution/tree/rvmaster/checkstyle-tester as a starting point, namely the logic from launch_diff.sh to generate reports using checkstyle, not maven-checkstyle-plugin.