RFR: 7903502: JOL: Revisit rounding in "heap-estimates" report

[Aleksey Shipilev]

Issue in "heapdump-estimates" report: the rounding to zero should not produce "0.0%", which might be confusing.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jol/pull/43/files
 Webrev: https://webrevs.openjdk.org/?repo=jol&pr=43&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903502
  Stats: 242 lines in 3 files changed: 90 ins; 22 del; 130 mod
  Patch: https://git.openjdk.org/jol/pull/43.diff
  Fetch: git fetch https://git.openjdk.org/jol.git pull/43/head:pull/43

PR: https://git.openjdk.org/jol/pull/43