Text-finder Plugin
This plugin lets you search keywords in the files you specified and use that to downgrade a "successful" build to be unstable or a failure.
This is handy when you have some tools in your build chain that don't use the exit code properly.
The search is always performed, even on builds which returned a non-zero exit status, but the reclassification only applies to builds which returned an overall exit status of zero.
See the documentation and release notes at Text-finder Plugin on the Jenkins Wiki for more information.