RFR: 8257722: Improve "keytool -printcert -jarfile" output [v3]

[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:

  Update output per review comment

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6126/files
  - new: https://git.openjdk.java.net/jdk/pull/6126/files/02f723d5..85b3cf46

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6126&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6126&range=01-02

  Stats: 130 lines in 4 files changed: 82 ins; 23 del; 25 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