RFR: JDK-8247353: jtreg tests minor issues clean up

[Alexey Semenyuk]

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

Minor jpackage jtreg tests clean up of issues uncovered during the 
recent local test runs.

- Alexey

[1] https://bugs.openjdk.java.net/browse/JDK-8247353

[2] http://cr.openjdk.java.net/~asemenyuk/8247353/webrev.00