RFR: 8338153: java/awt/Checkbox/CheckboxCheckerScalingTest.java test failed on linux machine

[Tejesh R]

Test failed intermittently on particular host. Though analysis pointed out to a test frame at left top on that host, I've updated the test for further stabilizing it. Two things done here:
1. Move the frame to center of the screen rather than left top.
2. Added tolerance checks for color comparison - this is based on analysis reports where the image didn't had exact black color which is supposed to be. So like other test cases, providing some tolerance for comparison.

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Commit messages:
 - Adding tolerance for comparison + position change

Changes: https://git.openjdk.org/jdk/pull/20723/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20723&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338153
  Stats: 10 lines in 1 file changed: 9 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20723.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20723/head:pull/20723

PR: https://git.openjdk.org/jdk/pull/20723