java dependency and .{deb,rpm} dependency

I'm not sure of the best way to handle this, but when I was installing elasticsearch I forgot to install java and was a little perplexed about what why a simple

```ruby
class {"elasticsearch": }
```

wasn't working. As a starting point, I added an example in the README to show how to install the latest and greatest elasticsearch (currently 0.90.2), as [illustrated in this gist](https://gist.github.com/wingdspur/2026107). 

A more involved solution would 
1. fail gracefully if java is not detected on the machine with a user-friendly error message directing the user to the README, and
2. automatically download the .{deb,rpm} file automatically if the $pkg_source isn't specified so that the bare-bones elasticsearch command works as you'd (or at least "I'd") expect.

I'm happy to contribute these changes if that sounds of interest, but thought I'd post a quick fix in the meantime to start a discussion in case others have ideas about how to address this.