Add test-lock-factory to Gradle build

When porting to Gradle, the following task was missed to be ported to Gradle:
https://github.com/apache/lucene-solr/blob/92139985c3eeb80adb8af345e61a3090d30430a5/lucene/core/build.xml#L148-L234

This is somehow an integration test. It's not part of the test suite, as the code is part of main distribution and is a client-server implementation that has one coordinator to handle other JVMs to hammer a directories' lock factory.

It may be included into the test suite, but as it spawns multiple JVMs (thats essential for it to work), I see this as a separate thing.

I would like to implement that snippet of ANT code in Gradle and attach it to :lucene:core's test task. If we have an integration test framework at some point we can make a real integTest out of it, but for now a simple Groovy script is fine.