<Swing Dev> RFR: 8202880: Test javax/swing/JPopupMenu/8075063/ContextMenuScrollTest.java fails

[Prasanta Sadhukhan]

This test was unstable in linux in nightly testing. Modified to move the frame to center of screen so that the left-taskbar of linux doesn't interfere with the mouse movement along with delay after frame is visible to make it more stable. 
Mach5 job running for several iterations on all platforms is ok. Link in JBS.

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Commit messages:
 - 8202880: Test javax/swing/JPopupMenu/8075063/ContextMenuScrollTest.java fails

Changes: https://git.openjdk.java.net/jdk/pull/2061/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2061&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8202880
  Stats: 48 lines in 2 files changed: 9 ins; 22 del; 17 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2061.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2061/head:pull/2061

PR: https://git.openjdk.java.net/jdk/pull/2061