RFR: 8274205: Handle KDC_ERR_SVC_UNAVAILABLE error code from KDC [v2]

[Alexey Bakhtin]

> The code change handles KDC_ERR_SVC_UNAVAILABLE error code (29) received from KDC and resends the initial request to the next KDC in the list. It aligns error code handling with the MIT Kerberos implementation.
> sun/security/krb5 tests passed

Alexey Bakhtin has updated the pull request incrementally with one additional commit since the last revision:

  Added Unavailable test

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5658/files
  - new: https://git.openjdk.java.net/jdk/pull/5658/files/6bf7dfc0..96774140

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5658&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5658&range=00-01

  Stats: 80 lines in 1 file changed: 80 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5658.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5658/head:pull/5658

PR: https://git.openjdk.java.net/jdk/pull/5658