progress.c tests: test some invalid usage

progress.c tests: test some invalid usage

Test what happens when we "stop" without a "start", omit the "stop"
after a "start", or start two concurrent progress bars. This
extends the trace2 tests added in 98a13647408 (trace2: log progress
time and throughput, 2020-05-12).

These tests are not merely testing the helper, but invalid API usage
that can happen if the progress.c API is misused.

The "without stop" test will leak under SANITIZE=leak, since this
buggy use of the API will leak memory. But let's not skip it entirely,
or use the "!SANITIZE_LEAK" prerequisite check as we'd do with tests
that we're skipping due to leaks we haven't fixed yet. Instead
annotate the specific command that should skip leak checking with
custom $LSAN_OPTIONS[1].

1. https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer

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