RFR: 8305778: javax/swing/JTableHeader/6884066/bug6884066.java: Unexpected header's value; index = 4 value = E

[Prasanta Sadhukhan]

Although not reproducible locally or in mach5, some stability fixes have been added in the test like
induce 1s delay after frame is made visible, increase autodelay time, move frame to center of screen and also dispose frame at end.

Modified test pass for several iterations in all platforms. Link in JBS

-------------

Commit messages:
 - 8305778: javax/swing/JTableHeader/6884066/bug6884066.java: Unexpected header's value; index = 4 value = E
 - 8305778: javax/swing/JTableHeader/6884066/bug6884066.java: Unexpected header's value; index = 4 value = E

Changes: https://git.openjdk.org/jdk/pull/13417/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13417&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305778
  Stats: 61 lines in 1 file changed: 26 ins; 8 del; 27 mod
  Patch: https://git.openjdk.org/jdk/pull/13417.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13417/head:pull/13417

PR: https://git.openjdk.org/jdk/pull/13417