RFR: 8283724: Incorrect description for jtreg-failure-handler option

[KIRIYAMA Takuya]

The description for the jtreg-failure-handler option is incorrect, so I fixed it to describe jtreg-failure-handler option.  
Would you please review this fix?

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Commit messages:
 - 8283724: Incorrect description for jtreg-failure-handler option

Changes: https://git.openjdk.java.net/jdk/pull/9099/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=9099&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8283724
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/9099.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/9099/head:pull/9099

PR: https://git.openjdk.java.net/jdk/pull/9099