Merge remote-tracking branch 'upstream/master'
additional assertions in test cases to check if links are available and implemented test cases for issue 21723 (problem exists in checkstyle, pmd and findbugs)
[FIXED JENKINS-22988] handle the case when Dockerfile is packaged inside a jar file
Better to keep the image name clean and use tag for the hash
better way to combine a path
Removed a pointless method that's only used from one place.

I also don't see the need for 1sec wait
[FIXED JENKINS-22990]

Don't require the update center metadata to be present.
[maven-release-plugin] prepare release acceptance-test-harness-1.2
[maven-release-plugin] prepare for next development iteration
reformated and changed
Merge branch 'link_checks' of https://github.com/jenkins-acceptance-test-group/acceptance-test-harness
[JENKINS-22989]

Enabled JavaScript for HtmlUnit.
[JENKINS-21723] Mark test case that exposes the bug as ignored.
Merge branch 'master' of github.com:jenkinsci/acceptance-test-harness