RFR: 8292763: JDK-8292716 breaks configure without jtreg

[Magnus Ihse Bursie]

The fix for JDK-8292716 was supposed to verify version number requirements for jtreg. Unfortunately, it breaks configure if no jtreg is supplied.

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Commit messages:
 - 8292763: JDK-8292716 breaks configure without jtreg

Changes: https://git.openjdk.org/jdk/pull/9975/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9975&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292763
  Stats: 14 lines in 1 file changed: 1 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/9975.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9975/head:pull/9975

PR: https://git.openjdk.org/jdk/pull/9975