RFR: 7903792: ReportOnlyTest may fail in "headless" environments [v2]

[Jonathan Gibbons]

> Please review a test-only fix to the problems observed running `ReportOnlyTest.gmk`, as seen in some GitHub actions for other PRs. 
> 
> The general problem that is addressed is inconsistent determination of a "headless" environment, as determined by `Basic.java` and as given by an env variable when running the tests. 
> 
> More details are given in the test itself.

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  display ReportOnlyTest jt.log

-------------

Changes:
  - all: https://git.openjdk.org/jtreg/pull/223/files
  - new: https://git.openjdk.org/jtreg/pull/223/files/ac8582d9..d17d1b37

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=223&range=01
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=223&range=00-01

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jtreg/pull/223.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/223/head:pull/223

PR: https://git.openjdk.org/jtreg/pull/223