Message Title

When Lucene's website is down (happened today for all of Apache's websites), or has a transient failure (happens from time to time, say every month or so), we get this warning:

[INFO]
1 warning
[WARNING] Javadoc Warnings
[WARNING] javadoc: warning - Error fetching URL: http://lucene.apache.org/core/8_4_1/core/

[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  03:55 min
[INFO] Finished at: 2020-02-04T07:28:49Z
[INFO] ------------------------------------------------------------------------
[INFO] [jenkins-event-spy] Generated /mnt/jenkins-workdir/workspace/hibernate-search_master@tmp/withMaven467ad2c1/maven-spy-20200204-072453-6633316077978698606787.log
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-javadoc-plugin:3.1.0:javadoc-no-fork (generate-javadoc) on project hibernate-search-backend-lucene: An error has occurred in Javadoc report generation: Project contains Javadoc Warnings -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
[ERROR] 
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR]   mvn <args> -rf :hibernate-search-backend-lucene

Failing on javadoc warnings makes sense: it means we won't generate invalid javadoc, or at least it makes it less likely. What makes less sense is relying on external infrastructure (other than our CI and Maven Central) during our build.

Ideally we would generate links without actually accessing the website. offlineLinks looks like what we need.