<AWT Dev> RFR: 8198619: java/awt/Focus/FocusTraversalPolicy/ButtonGroupLayoutTraversal/ButtonGroupLayoutTraversalTest.java fails on mac

[Prasanta Sadhukhan]

This test was failing in CI nightly testing due to samevm mode issue. 
Modified test to use waitForIdle() judiciously, dispose frame in finally block and move the frame to center of screen.
Several iterations of the test pass in all platforms. Link in JBS.

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Commit messages:
 - Fix
 - 8198619: java/awt/Focus/FocusTraversalPolicy/ButtonGroupLayoutTraversal/ButtonGroupLayoutTraversalTest.java fails on mac

Changes: https://git.openjdk.java.net/jdk/pull/3618/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3618&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8198619
  Stats: 76 lines in 2 files changed: 26 ins; 20 del; 30 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3618.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3618/head:pull/3618

PR: https://git.openjdk.java.net/jdk/pull/3618