RFR: 6859027: Duplicate communications to KDC in GSSManager.createCredential(usage)

[Weijun Wang]

A one slot ccache is added to avoid multiple authentication from the same principal.

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Commit messages:
 - 6859027: Duplicate communications to KDC in GSSManager.createCredential(usage)

Changes: https://git.openjdk.java.net/jdk/pull/5286/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5286&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-6859027
  Stats: 114 lines in 2 files changed: 110 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5286.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5286/head:pull/5286

PR: https://git.openjdk.java.net/jdk/pull/5286