Upgrade Guava to latest

As part of STORM-3311, I want to use https://google.github.io/guava/releases/23.0/api/docs/com/google/common/io/MoreFiles.html to replace Guava's Files class. We're currently on Guava 16.0.1, which is too old. Since we're shading Guava, there shouldn't be an issue with upgrading it. Modules like storm-cassandra that require old Guava versions can depend directly on unshaded Guava in the version they like.