Revamp Java cookbook and add support for Oracle JDK8 (EA Edition)

@joshk @michaelklishin: could you please test this one on your side?

Yeah, I know that there is quite a bunch of changes here, but believe me it is quite solid and should ease the cookbook maintenance in the future. Adding JDK8 without refactoring was too painful, I have been very prudent to keep in sync with precedent behavior on Ubuntu 12.04. 

The only thing that significantly changed is that now the Oracle JDKs also use the Ubuntu certificate keystore, but that can be changed if another option is preferred.

**Attention:** the chef run_lists must be adapted... I'll submit a PR on travis-images right now...

Related to travis-ci/travis-ci#1330 and travis-ci/travis-ci#1291