RFR: JDK-8232279: Improve test helpers #2

[Alexey Semenyuk]

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

This is a fix for the JDK-8200758-branch branch of the open sandbox 
repository (jpackage).

Additionally migrated some tests that used the old test helpers to use 
the new test helpers.

- Alexey

[1] https://bugs.openjdk.java.net/browse/JDK-8232279

[2] http://cr.openjdk.java.net/~asemenyuk/8232279/webrev.00/