RFR: 6854300: [TEST_BUG] java/awt/event/MouseEvent/SpuriousExitEnter/SpuriousExitEnter_3.java fails in jdk6u14 & jdk7

[Alexander Zvegintsev]

Test trying to call `button.getLocationOnScreen()` when its frame not yet fully configured, so the obtained button location is shifted by window's height. 

Waiting a bit after `setVisible()` call fixes the issue. Some cleanup was made also. Testing is green on all platforms.

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Commit messages:
 - EDT
 - initial

Changes: https://git.openjdk.java.net/jdk/pull/6164/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6164&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-6854300
  Stats: 61 lines in 2 files changed: 32 ins; 4 del; 25 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6164.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6164/head:pull/6164

PR: https://git.openjdk.java.net/jdk/pull/6164