RFR: CODETOOLS-7903183: Log start time for every action

[Jonathan Gibbons]

Please review a small update to provide start and end times for each action in a .jtr file, to help better track "unaccounted" time.

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Commit messages:
 - CODETOOLS-7903183: Log start time for every action

Changes: https://git.openjdk.java.net/jtreg/pull/85/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=85&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903183
  Stats: 8 lines in 1 file changed: 6 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/85.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/85/head:pull/85

PR: https://git.openjdk.java.net/jtreg/pull/85