RFR: 7903793: Latent typo in ReportOnlyTest.gmk [v2]

[Jonathan Gibbons]

> Please review a test-only fix for a mistake in `ReportOnlyTest.gmk`.
> 
> The report directory previously had a double prefix of the value of `$(BUILDTESTDIR)`

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

  address review feedback

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

Changes:
  - all: https://git.openjdk.org/jtreg/pull/222/files
  - new: https://git.openjdk.org/jtreg/pull/222/files/8bca34ac..4e3599d5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=222&range=01
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=222&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtreg/pull/222.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/222/head:pull/222

PR: https://git.openjdk.org/jtreg/pull/222