RFR: 7903318: Make -report:executed the default

[Daniel Jeliński]

Please review this change to the default value of `reportMode` property.

The proposed report mode produces a report on the selected tests only; it is very fast to execute, and usually completes under a second.
The current default mode produces a report on all tests in the same test suite. It requires scanning all directories and source files in the test suite, requires a long time to produce, and usually produces the same results when jtreg is invoked from make.

If this change is integrated, the old report mode will be available under command line option `-report:all-executed`

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Commit messages:
 - Report executed tests by default

Changes: https://git.openjdk.org/jtreg/pull/123/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=123&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903318
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtreg/pull/123.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/123/head:pull/123

PR: https://git.openjdk.org/jtreg/pull/123