Java Buildpack v2.4

This change updates the Java Buildpack to version 2.4.  Version
2.4 has the following highlights:

* Configurable Access Logging in Tomcat (via Guillaume Berche)
* Session Replication working with Pivotal Redis Service (via John McTeague)

Both the online and offline buildpacks are updated as part of this
change.
Merge remote-tracking branch 'origin/pr/437' into develop