[COOK-3541] Java cookbook installs both JDK 6 and JDK 7 when JDK 7 is specified

https://tickets.opscode.com/browse/COOK-3541

This request is technically a dupe of #43, but since I didn't feel comfortable opening a COOK ticket for someone else's pull, and I have no way of knowing whether or not all the committers on that pull have signed the CLA, I redid the work and opened this pull request. Feel free to close it in favor of #43.