Gives the major version of the Java release (ie. Java 1.7.0_71, major version is 7) We also want to specifically return nil when java not present
Lets keep it vaguely consistent
java_version
Adapted from the many found on Github, simply runs `java -version` and strips the results. From what I can find there aren't many edge cases for the result `java -version 2>&1` could return, so this should be fairly compatible.