test-lib.sh: use "Bail out!" syntax on bad SANITIZE=leak use

test-lib.sh: use "Bail out!" syntax on bad SANITIZE=leak use

Improve the "GIT_TEST_PASSING_SANITIZE_LEAK=true" test mode added in
956d2e4639b (tests: add a test mode for SANITIZE=leak, run it in CI,
2021-09-23) to use a TAP "Bail out!" message when exiting. This will
cause the test run to exit immediately under a TAP consumer like
"prove(1)".

See 614fe015212 (test-lib: bail out when "-v" used under "prove",
2016-10-22) for the initial introduction of "Bail out!" to the
--verbose being amended here.

Before this compiling with "SANITIZE=" and running the tests with
"prove(1)" would cause all the tests to be run to the end (output
trimmed for fewer columns):

    $ GIT_TEST_PASSING_SANITIZE_LEAK=true make
    rm -f -r 'test-results'
    *** prove ***
    t0000-basic.sh ......... Dubious, test returned 1 (wstat 256, 0x100)
    No subtests run
    t0001-init.sh .......... Dubious, test returned 1 (wstat 256, 0x100)
    No subtests run
    [...output where we list every single t[0-9]*.sh file as failing snipped]

Whereas now we'll fail early, like this ("->" line wrapping added):

    $ GIT_TEST_PASSING_SANITIZE_LEAK=true make
    [...]

    t0000-basic.sh ..................................... Bailout called.  Further testing stopped:
    -> GIT_TEST_PASSING_SANITIZE_LEAK=true has no effect except when compiled with SANITIZE=leak
    FAILED--Further testing stopped: GIT_TEST_PASSING_SANITIZE_LEAK=true has no effect except
    -> when compiled with SANITIZE=leak
    make: *** [Makefile:53: prove] Error 1

This change also adds a red color to the "Bailout called" line, as
we're now using "say_color error". That improves existing output in
the case of e.g.:

    $ prove -j8 t[0-9]*.sh :: -v
    Bailout called.  Further testing stopped:  verbose mode forbidden under TAP harness; try --verbose-log
    FAILED--Further testing stopped: verbose mode forbidden under TAP harness; try --verbose-log

We don't need to have a "Bail out! " prefix when we're not running
under a TAP consumer (i.e. if test -n "$HARNESS_ACTIVE"), but let's
not make the output conditional on that. Showing it under e.g.:

    $ GIT_TEST_PASSING_SANITIZE_LEAK=true ./t0095-bloom.sh
    Bail out! GIT_TEST_PASSING_SANITIZE_LEAK=true has no effect except when compiled with SANITIZE=leak

Doesn't harm anything, and I don't think the (small) complexity of
only adding this if we're under "$HARNESS_ACTIVE" is worth it.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>