RFR: 8279064: New options for ktab to provide non-default salt

[Weijun Wang]

Please review this enhancement and its [CSR](https://bugs.openjdk.java.net/browse/JDK-8279632). Two new options `-s salt` and `-f` can be specified on the `ktab` command when adding entries.

I'm a little concerned about the compatibility risk described in the CSR, i.e. the `-f` option is already used in `ktab -d` to force removing entries. Hopefully not many people writing their own wrappers on ktab that always include the `-f` option. I do want to be consistent with the naming in the MIT krb5 ktutil command.

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Commit messages:
 - 8279064: New options for ktab to provide non-default salt

Changes: https://git.openjdk.java.net/jdk/pull/6991/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6991&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279064
  Stats: 155 lines in 5 files changed: 135 ins; 1 del; 19 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6991.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6991/head:pull/6991

PR: https://git.openjdk.java.net/jdk/pull/6991