Add is_linux java check to locate.py

Following http://stackoverflow.com/questions/5251323/where-can-i-find-the-java-sdk-in-linux
this was tested on Ubunutu/13.04. Java location is:
```
$ readlink -f `which java`
/usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java
```