[ci] Clean up Jenkinsfile

[driazati]

This doesn't change any functionality but cleans up how we define things in CI by factoring out the common steps into a function. There are several instances were we weren't marking things skipped consistently or applying timeouts, so this should make that easier. There are also some random style changes to make groovylint happy

cc @areusch

[areusch]

i think i still prefer the templated approach here, to be honest. while i think that logic like this eases high-level comprehension, it adds another layer of abstraction over what Jenkins is actually doing, so it makes it harder to debug problems:

    if (args.condition) {
      node(args.node_type) {
        ws(per_exec_ws(args.ws_name)) {
          timeout(time: max_time, unit: 'MINUTES') {
            init_git()
            if (args.junit) {
              try {
                args.script()
              } finally {
                junit 'build/pytest-results/*.xml'
              }
            } else {
              args.script()
            }
          }
        }
      }
    } else {
      Utils.markStageSkippedForConditional(args.name)
    }
  }
}

perhaps we could reconsider this as a templated approach once #10425 lands?

[areusch]

er I should have said now that #10425 has landed.