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

[Hai-May Chao]

> 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

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6126/files
  - new: https://git.openjdk.java.net/jdk/pull/6126/files/ba4bb4b7..02f723d5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6126&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6126&range=00-01

  Stats: 46 lines in 1 file changed: 0 ins; 45 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6126.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6126/head:pull/6126

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