8370156: Fix jpackage IconTest

[alexeysemenyukoracle]

Rework IconTest.

Verified it produces the output as expected.

It still will not catch JDK-8370155. However, this is deliberate to avoid significant changes in the test and implementation in a single commit.

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Progress

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Issue

• JDK-8370156: Fix jpackage IconTest (Bug - P4)

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[bridgekeeper]

👋 Welcome back asemenyuk! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@alexeysemenyukoracle this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout JDK-8370156
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

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Webrevs

• 01: Full (112d042f)
• 00: Full (720946df)

[alexeysemenyukoracle]

@sashamatveev PTAL