Make idempotent and update to standard Java install paths

Happy to discuss these changes as they're a little larger, but I found that the module wasn't idempotent as `rpm -i <whatever>.rpm` doesn't exit with code 0 if the package is already installed. So I updated the `creates` lines to point to the standard java install paths (`/usr/java/<version>`) and made sure they (wit the right version number) prevent the reinstall from happening. I also moved some parameters around to make it easier to add support for other java versions in future.