RFR: JDK-8247422: --runtime-image on Mac should work for runtime root

[Alexey Semenyuk]

Please review fix [2] for jpackage bug [1].

Restore handling not only Java runtime home but also Java runtime root 
directory in `--runtime-image` option on Mac.
The patch also fixes [3] issue as a side effect of moving functionality 
of BasicTest.testJLinkRuntime() function into the new 
CookedRuntimeTest.test().

- Alexey

[1] https://bugs.openjdk.java.net/browse/JDK-8247422

[2] http://cr.openjdk.java.net/~asemenyuk/8247422/webrev.00

[3] https://bugs.openjdk.java.net/browse/JDK-8247424