RFR: 8282511: Use fixed certificate validation date in SSLExampleCert template

Tue Mar 1 22:44:31 UTC 2022

May I have this test update reviewed?

The certificates used in SSL testing template SSLExampleCert could expired in the future (for example [JDK-8282398](https://bugs.openjdk.java.net/browse/JDK-8282398).  It is not always easy to replace the certificates if the template has been used a lot.

This update is trying to use a fixed validation date, so that even the certificates are expired the test will continue to work with no surprises.

I also did a few code clean up in this patch.

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Commit messages:
 - 8282511: Use fixed certificate validation date in SSLExampleCert template

Changes: https://git.openjdk.java.net/jdk/pull/7651/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7651&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282511
  Stats: 217 lines in 2 files changed: 35 ins; 2 del; 180 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7651.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7651/head:pull/7651

PR: https://git.openjdk.java.net/jdk/pull/7651