Run gradle build without running tests

Gradle doesn't really expose an option for you to run your build without running tests. We were able to make this work by looking for an environment variable:

checkstyleMain.onlyIf { !System.getenv('SKIP_TESTS') }
checkstyleTest.onlyIf { !System.getenv('SKIP_TESTS') }
compileTestJava.onlyIf { !System.getenv('SKIP_TESTS') }
jacocoTestCoverageVerification.onlyIf { !System.getenv('SKIP_TESTS') }
test.onlyIf { !System.getenv('SKIP_TESTS') }

This means I can run, for example, SKIP_TESTS=true gradle build and it won't complain about checkstyle errors.