RFR: 8245601: [TESTBUG] Disable TabPaneDragPolicyTest on Mac until JDK-8213136 is fixed and fix ISE

Fri May 22 13:27:43 UTC 2020

The reordering tests in TabPaneDragPolicyTest fail only fails on Mac. It may be a a product issue which is tracked by
[JDK-8213136](https://bugs.openjdk.java.net/browse/JDK-8213136). This PR disables the 4 reordering test on Mac
platform. And fixes an Exception, Please check the JBS for exception.

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Commit messages:
 - 8245601: [TESTBUG] Disable TabPaneDragPolicyTest on Mac until JDK-8213136 is fixed and fix ISE

Changes: https://git.openjdk.java.net/jfx/pull/234/files
 Webrev: https://webrevs.openjdk.java.net/jfx/234/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8245601
  Stats: 13 lines in 1 file changed: 11 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/234.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/234/head:pull/234

PR: https://git.openjdk.java.net/jfx/pull/234