RFR: 8257722: Improve "keytool -printcert -jarfile" output [v2]

[Weijun Wang]

On Wed, 27 Oct 2021 16:32:48 GMT, Hai-May Chao <hchao at openjdk.org> wrote:

>> This change does a few improvements to the output of `keytool -printcert -jarfile` command to help readability and diagnosis.
>
> Hai-May Chao has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Updated TimestampCheck test and removed its unused methods

One new comment: Now that if there is only one cert, there is no need to write `Certificate #n of m`. If there's only one signer, we also don't need to write `of signer #n`.

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PR: https://git.openjdk.java.net/jdk/pull/6126