<Swing Dev> RFR: 8028707: javax/swing/JComboBox/6236162/bug6236162.java fails on azure

[Prasanta Sadhukhan]

Please review a test fix for a test issue seen in nightly testing where the combobox selection was not happening
properly.  It seems the issue seems to stem from the fact that the test was not waiting for frame to be visible long
enough before commencing robot actions. Added robot delay and remove the dependancy on Util class.
Mach5 job was run for several iteration on all 3 platforms. Link in JBS

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Commit messages:
 - 8028707: javax/swing/JComboBox/6236162/bug6236162.java fails on azure

Changes: https://git.openjdk.java.net/jdk/pull/686/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=686&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8028707
  Stats: 16 lines in 2 files changed: 7 ins; 6 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/686.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/686/head:pull/686

PR: https://git.openjdk.java.net/jdk/pull/686