(packaging)(#21631) Update packaging to use Java 1.7 as the default

As Java 1.6 is being deprecated, we would like to start using Java 1.7 by default for PuppetDB.

As Java 1.7 is available on all RPM-based platforms that we support (>= EL5, >= Fedora 17), this PR removes the dependency on Java 1.6 from the packaging artifacts.

Since Java 1.7 is not available in the default repos for Debian Squeeze or Ubuntu Lucid, use Java 1.7 if it's available, and fall back to Java 1.6 if it is not.