Fixes for centos versions

While working on Centos support for https://github.com/garethr/riemann-vagrant I noticed that just using: 

    include java

Would fail on Centos 5.8 and 6.3 (using the Puppetlabs provided vagrant boxes) with an incorrect package name. The README indicates this module supports 5.3.

Checking those two boxes using yum seems to indicate that the openjdk packages are available so I've added additional logic to detect those specific versions of Centos and if found choose a relevant package in to the same way as the ubuntu logic.

I've also added tests just for this functionality (the module previously had no test suite). Two of the tests verify the backwards compatibility for 5.3, the other two the new (working) behaviour for 5.8. and 6.3.