<AWT Dev> RFR: 8250804: Can't set the application icon image for Unity WM on Linux.

[Alexander Zvegintsev]

As of now we can have two icons: on the side dock and on the top bar.
But this test was written for an old time Unity with an icon in the side dock only. 

Icon at the top by default is displayed as grayscale(the actual reason of submitting bug report).
BTW it may not be presented depending on Gnome Shell settings.

`setIconImage()` seems to be working as expected in this case, but we need to clarify the test's instruction.

Besides that the test has another issue: it does not fail on pressing "Fail" button. It is also fixed.

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Commit messages:
 - ProblemList
 - initial

Changes: https://git.openjdk.java.net/jdk/pull/2838/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2838&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8250804
  Stats: 22 lines in 2 files changed: 9 ins; 5 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2838.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2838/head:pull/2838

PR: https://git.openjdk.java.net/jdk/pull/2838