PDB-128: Support Oracle Java distribution.

On Debian it's possible to package releases from Oracle through
make-jpkg, a utility provided by the java-package package:
https://wiki.debian.org/JavaPackage

This commit adds support for:
 * Detecting Oracle Java 1.7 packaged RE or SDK
 * Satisfy the package requirement of Java by looking for the j2re1.7
   provides that the make-jpkg packages carry, both RE and SDK.

I've left out satisfying the dependency through j2re1.6 as @kbarber
and I agreed that we shouldn't promote the usage of Java 1.6 any
further.
Merge pull request #793 from daenney/debian-java-1.6.x

PDB-128: Support Oracle Java distribution.