Add Java alternatives for RHEL based distros.

This is a followup to pull request #61.

The code was contributed by @dstockman on the PR referenced above.

The reason I did not include the java alternative updates in java::params is because the default RPM packages for openJDK automatically set the java alternatives when installed. The only time this would be used is when installing an alternative package suck as Oracle Java.

@mhaskel