Add java 7 support

This works fine with Java 7 (with this pull request) provided the following changes are made:

The zipfile hosted at https://s3.amazonaws.com/promojam-devops/packages/java/UnlimitedJCEPolicyJDK7.zip extracts into a directory "UnlimitedJCEPolicyJDK7" which isn't compatible with this recipe because it assumes the files extract into /tmp/jce - I re-packaged the zipfile so it extracts into jce here: http://gloo.ops.s3.amazonaws.com/jce.zip - you can do the same and replace the default attributes with that location to fix the extract issue. 

The PR also changes the reference to jdk_version to a string so that the url / checksum are properly referenced. 

This recipe was tested under the following versions of chef using jdk 7 via the java cookbook:
- 10.20.0 (ubuntu 12.04)
- 11.4.0 (ubuntu 12.04)