Fix JENKINS-20384

Added more information to the help files.
Fix JENKINS-22041

Added check to see if any tests failed this time that didn't fail last
time
Merge branch 'master' of github.com:jenkinsci/email-ext-plugin
Update to latest LTS in pom.xml and fix tests for new JenkinsRule visibility (before, after)
Merge branch 'master' of github.com:jenkinsci/email-ext-plugin