Checkstyle Test Coverage tool should ignore everything in the .gitignore of the repository it's invoked in

[alexjpwalker]

Repositories such as client-nodejs, which generate large amounts of (ignored) files in the source folder when compiled, are difficult for tool/checkstyle/test-coverage to analyse because they contain so many files.

We already work around this problem by excluding specific named folders and files from the checkstyle coverage test, as follows:

workspace_files, _ = tc.shell_execute([
        'find', '.',
            '(', '-name', '.git',
            '-o', '-name', '.idea',
            '-o', '-name', '.ijwb',
            '-o', '-name', '.github',
            '-o', '-name', '.bazelversion',
            '-o', '-name', '.gitkeep',
            '-o', '-name', 'VERSION',
            '-o', '-name', '*.md',
            '-o', '-name', 'node_modules',
        ')', '-prune', '-o', '-type', 'f', '-print'
    ], cwd=os.getenv("BUILD_WORKSPACE_DIRECTORY"))

but this is woefully unmaintainable and would be much nicer if it parsed the .gitignore file.