parallel-tests: simplify testsuite summary

parallel-tests: simplify testsuite summary

Prefer a more deterministic, "tabular" format for the testsuite
summary, always listing the numbers of passed, failed, xfailed,
xpassed, skipped and errored tests, even when these numbers are
zero.  This simplify the logic of testsuite summary creation,
makes it more easily machine-parseable, and will probably allow
for easier addition of new kinds of test results in the future.

* lib/am/check.am (am__tty_colors_dummy): New make variable, to
reduce code duplication.  Extracted from previous versions of
$(am__tty_colors), and extended by defining two new variables
`$mgn' and `$brg'.
[%?COLOR%, %!?COLOR%] (am__tty_colors): Use that new variable.
(am__text_box): Delete, is not needed anymore.
($(TEST_SUITE_LOG)): Rewrite associated rules to implement the
new testsuite summary format.
* NEWS: Update.
* tests/check10.test: Don't run with the parallel-tests harness
too, that makes no sense anymore.
* tests/color.test: Update and adjust.
* tests/color2.test: Likewise.
* tests/parallel-tests.test: Likewise.
* tests/parallel-tests3.test: Likewise.
* tests/parallel-tests6.test: Likewise.
* tests/parallel-tests9.test: Likewise.
* tests/parallel-tests-unreadable-log.test: Likewise.
* tests/parallel-tests-empty-testlogs.test: Likewise.
* tests/parallel-tests-log-override-recheck.test: Likewise.
* tests/parallel-tests-no-spurious-summary.test: Likewise.
* tests/test-driver-custom-multitest.test: Likewise.
* tests/test-driver-end-test-results.test: Likewise.
* tests/parallel-tests-no-color-in-log.test: New test.
* tests/testsuite-summary-color.test: Likewise.
* tests/testsuite-summary-count.test: Likewise.
* tests/testsuite-summary-count-many.test: Likewise.
* tests/testsuite-summary-reference-log.test: Likewise.
* tests/testsuite-summary-checks.sh: New auxiliary script, used
by the new tests above.
* tests/extract-testsuite-summary: Likewise.
* tests/trivial-test-driver: Optimize for speed when there are
lots of of tests.
* tests/Makefile.am (EXTRA_DIST): Distribute them.
(testsuite-summary-color.log, testsuite-summary-count.log): Depend
on them.
(testsuite-summary-count-many.log): Depend on the auxiliary scripts
'trivial-test-driver' and 'extract-testsuite-summary'.
(TESTS): Update.