RFR: 8247690: RunTest does not support running of JTREG manual tests

[Matthew Donovan]

This PR adds a make keyword, MANUAL, to run manual tests with the make command e.g.:


make test JTREG=MANUAL=true TEST=... 


I've gotten into the habit of running tests with make and although this doesn't come up often, I have wanted the functionality for a while.

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Commit messages:
 - 8247690: RunTest does not support running of JTREG manual tests

Changes: https://git.openjdk.org/jdk/pull/28381/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28381&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8247690
  Stats: 8 lines in 1 file changed: 6 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28381.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28381/head:pull/28381

PR: https://git.openjdk.org/jdk/pull/28381