Launch/Diff Groovy should remove use of maven-checkstyle-plugin

See https://issues.apache.org/jira/browse/MCHECKSTYLE-346 .
We need to deprecate all usage of `maven-checkstyle-plugin` so we can start implementing backward breaking changes.

The groovy scripts are our heaviest scripts as we use them for all types of regression, so they should be the first ones converted.

Instead of installing checkstyle and then running `mvn site`, we should package the project into the `all` jar and run the CLI checkstyle program and produce the XML violation file. This file and the sources will be what is fed into `patch-diff-report-tool` to produce the final report.

We should not need to change `patch-diff-report-tool`. Using the CLI allows us to run Checkstyle on the repo directory directly instead of copying the files to another location temporarily. This will also allow us to run regression on non-Java files which is what `maven-jxr-plugin` forced on us.