Change default JVM location to /usr/lib/jvm/java-7-openjdk-amd64

Given that OpenJDK 1.7 is the recommended Java SDK for
Chromium these days, we should get rid of linking to the old
non-standardized link referring to a Sun Java 1.6 SDK.

Instead of requiring all users to set JAVA_HOME, I prefer
have the most common path as default and and close webrtc:2113
as won't fix after this is submitted.

BUG=2113
R=henrike@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/29839004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7584 4adac7df-926f-26a2-2b94-8c16560cd09d