RFR: 8292196: Reduce runtime of java.util.regex microbenchmarks

[Eric Caspole]

These changes reduce the run time to 45 minutes from about 1h40m with stability good enough for weekly promo build testing.

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Commit messages:
 - 8292196: Reduce runtime of java.util.regex microbenchmarks

Changes: https://git.openjdk.org/jdk/pull/9861/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9861&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292196
  Stats: 27 lines in 4 files changed: 4 ins; 14 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/9861.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9861/head:pull/9861

PR: https://git.openjdk.org/jdk/pull/9861