RFR: 8399: Fixing the IOPage tests

[Marcus Hirt]

[JMC-8370](https://bugs.openjdk.org/browse/JMC-8370) introduced an additional percentile, which now makes the UI tests fail.

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Commit messages:
 - 8399: Fixing the SocketIOPage tests

Changes: https://git.openjdk.org/jmc/pull/650/files
  Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=650&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8399
  Stats: 7 lines in 3 files changed: 2 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jmc/pull/650.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/650/head:pull/650

PR: https://git.openjdk.org/jmc/pull/650