RFR: 8017175: [TESTBUG] javax/swing/JPopupMenu/4634626/bug4634626.java sometimes failed on mac

[Alexander Zuev]

Moved Swing component modification to the EDT.
Increased wait time for popup to show up.
Made checking variabled volatile.
Generic code cleanup.
Removed the test from ProblemList.txt

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Commit messages:
 - 8017175: [TESTBUG] javax/swing/JPopupMenu/4634626/bug4634626.java sometimes failed on mac

Changes: https://git.openjdk.java.net/jdk/pull/6104/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6104&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8017175
  Stats: 48 lines in 2 files changed: 22 ins; 6 del; 20 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6104.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6104/head:pull/6104

PR: https://git.openjdk.java.net/jdk/pull/6104