RFR 8157931, jdk/internal/jrtfs/Basic.java fails with exploded builds

[Felix Yang]

Hi there,

    please review the following change.
Webrev:   http://cr.openjdk.java.net/~xiaofeya/8157931/webrev.00/

Bug:  https://bugs.openjdk.java.net/browse/JDK-8157931


The test "jdk/internal/jrtfs/Basic.java" fails when testing with 
exploded builds. It tried to access jrt-fs.jar which not exists in 
exploded builds.

In this fix, those tests will be skipped, if the build is identified as 
an exploded one. And please note that, a bug (JDK-8157936 
<https://bugs.openjdk.java.net/browse/JDK-8157936>) was found with the 
updated test.

Thanks,

Felix