RFR: 7902346: Need better message when test times out in agentvm mode

[Jaikiran Pai]

Can I please get a review of this change which proposes to improve the error message when a test action times out on an agent VM? This addresses https://bugs.openjdk.org/browse/CODETOOLS-7902346.

Before this change, whenever a test action timed out in an agentvm, then it would be reported as:

> result: Error. Agent error: java.lang.Exception: Agent 3 timed out with a timeout of 1200 seconds; check console log for any additional details 

With the changes in this PR, the error reporting will be a more accurate and won't give an impression that this was some error within the jtreg agent implementation. For `@run main ...`, the error will now say:

> result: Error. "main" action timed out with a timeout of 1200 seconds on agent 3

Another example, this time for a driver action:

> result: Error. "driver" action timed out with a timeout of 1200 seconds on agent 3

A couple of new self tests have been added to verify this change. Self tests including this new one continue to pass with this change.

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Commit messages:
 - 7902346: Need better message when test times out in agentvm mode

Changes: https://git.openjdk.org/jtreg/pull/205/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=205&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7902346
  Stats: 121 lines in 6 files changed: 114 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jtreg/pull/205.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/205/head:pull/205

PR: https://git.openjdk.org/jtreg/pull/205