Maven build fails to build Solr core tests due to missing dependency

If I run

ant get-maven-poms 
mvn -f maven-build/pom.xml install -DskipTests

On master or branch_8x, it fails to build the Solr tests due to a dependency on opentracing-mock.  Eclipse builds fine (because it uses a single classpath with everything in it), and not entirely sure how ant builds...

But the solr/core/ivy.xml doesn't have a dependency on opentracing-mock (though it has all the other opentracing modules)

https://github.com/apache/lucene-solr/pull/720 for the fix