[FIXED JENKINS-22850]

Added a checkbox in the pre-build-step configuration, to let the user
choose whether to stop the build or not in the case the of a failed
automatic rebase
Merge pull request #12 from vernyquartara/JENKINS-22850

[FIXED JENKINS-22850] [FIXED JENKINS-6851] Added option on "Automatic Rebase" action to fail the build when merge conflicts are found.