RFR: 7903741: some test properties are not documented [v2]

[Jonathan Gibbons]

> Please review a simple doc and test update for tag-spec.html, after it was recently noted that `test.module.path` was available but not documented.
> 
> The new test verifies 1:1 correspondence between names that are available, as env vars or system properties, and those that are documented.

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/203/files
  - new: https://git.openjdk.org/jtreg/pull/203/files/56c463c9..30e01190

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=203&range=01
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=203&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jtreg/pull/203.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/203/head:pull/203

PR: https://git.openjdk.org/jtreg/pull/203