[jdk11u-dev] RFR: 8270797: ShortECDSA.java test is not complete

[Goetz Lindenmaier]

I backport this for parity with 11.0.16-oracle.

I had to fix the call to HexFormat in one place. That class is not in 11.
Similar fix has been made before to the same test.

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Commit messages:
 - Backport 221e4b9c61cd1c9c3f4c037589ba639541532910

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/963/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=963&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270797
  Stats: 19 lines in 1 file changed: 18 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/963.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/963/head:pull/963

PR: https://git.openjdk.java.net/jdk11u-dev/pull/963