RFR: JDK-8214916: SourceLauncherTest fails on exploded image

[Jonathan Gibbons]

It is sometimes convenient during JDK development to use an "exploded 
image" instead of a linked image. But, a couple of javac tests contain a 
couple of test cases that don't work in this configuration.

The fix is simply to detect the situation and skip these test cases.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8214916
Webrev: http://cr.openjdk.java.net/~jjg/8214916/webrev/index.html