[jdk11u-dev] RFR: 8250839: Improve test template SSLEngineTemplate with SSLContextTemplate

[Goetz Lindenmaier]

I downport this for parity with 11.0.13-oracle.

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Commit messages:
 - Backport 473fa820007b59ecd676b292b3423fcd835712db

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/412/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=412&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8250839
  Stats: 320 lines in 1 file changed: 30 ins; 199 del; 91 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/412.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/412/head:pull/412

PR: https://git.openjdk.java.net/jdk11u-dev/pull/412