RFR: 8267751: (test) jtreg.SkippedException has no serial VersionUID

[Roger Riggs]

The class `test/lib/jtreg/SkippedException.java` is missing a serialVersionUID causing additional noise in compiler output of tests.

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

Commit messages:
 - Added serialVersionUID to jtreg.SkippedException to eliminate compilation warnings

Changes: https://git.openjdk.java.net/jdk/pull/4197/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4197&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267751
  Stats: 3 lines in 2 files changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4197.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4197/head:pull/4197

PR: https://git.openjdk.java.net/jdk/pull/4197