More code cleanup

[basil]

A series of code cleanup changes for this repository. Most of these changes fix IDE warnings from IntelliJ. I also reformatted the Javadocs and fixed several typos.

I kept each commit separate. Each commit message should be self-explanatory, but if anything is unclear I am happy to provide further explanation. Also, feel free to revert any specific cleanup commits that are unwanted.

[basil]

Looks like this change is exposing a pre-existing permissions issue in CasC tests:

+ java -jar plugins-compat-tester-cli/target/plugins-compat-tester-cli.jar -reportFile /home/jenkins/workspace/ries_plugin-compat-tester_PR-200/out/pct-report.xml -workDirectory /home/jenkins/workspace/ries_plugin-compat-tester_PR-200/out/work -skipTestCache true -mvn /home/jenkins/tools/hudson.tasks.Maven_MavenInstallation/mvn/bin/mvn -includePlugins configuration-as-code
Exception in thread "main" java.nio.file.AccessDeniedException/home/jenkins/workspace/ries_plugin-compat-tester_PR-200/out/work
	at java.base/sun.nio.fs.UnixException.translateToIOException(UnixException.java:90)
	at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:111)
	at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:116)
	at java.base/sun.nio.fs.UnixFileSystemProvider.createDirectory(UnixFileSystemProvider.java:385)
	at java.base/java.nio.file.Files.createDirectory(Files.java:689)
	at java.base/java.nio.file.Files.createAndCheckIsDirectory(Files.java:796)
	at java.base/java.nio.file.Files.createDirectories(Files.java:782)
	at org.jenkins.tools.test.PluginCompatTesterCli.main(PluginCompatTesterCli.java:65)
script returned exit code 1

This was always an issue but was being silently ignored due to the use of the legacy file API.

I'll temporarily add some ls -la statements to try and shed some more light on this.

[basil]

And, of course, the error went away on a subsequent re-run. I have now removed the debugging instrumentation I added and am trying another test run. It is frustrating that these CasC tests are so flaky. I would suggest that someone with write access to this repository consider migrating to Azure Container Instances, which offer a more deterministic build environment.

[oleg-nenashev]

Looks great, thanks+