The usual Scylla shutdown in a cluster test takes ~2.1s. 2s come from
```
co_await sleep(std::chrono::milliseconds(_gcfg.shutdown_announce_ms));
```
as the default value of `shutdown_announce_in_ms` is 2000. This sleep
makes every `server_stop_gracefully` call 2s slower. There are ~300 such
calls in cluster tests (note that some come from `rolling_restart`). So,
it looks like this sleep makes cluster tests 300 * 2s = 10min slower.
Indeed, `./test.py --mode=dev cluster` takes 61min instead of 71min
on the potwor machine (the one in the Warsaw office) without it.
We set `shutdown_announce_in_ms` to 0 for all cluster tests to make them
faster.
The sleep is completely unnecessary in tests. Removing it could introduce
flakiness, but if that's the case, then the test for which it happens is
incorrect in the first place. Tests shouldn't assume that all nodes
receive and handle the shutdown message in 2s. They should use functions
like `server_not_sees_other_server` instead, which are faster and more
reliable.
Improvement of the tests running time, so no backport. The fix of
`test_tablets_parallel_decommission` may have to be backported to
2026.1, but it can be done manually.
Closesscylladb/scylladb#28464
* github.com:scylladb/scylladb:
test: pylib: scylla_cluster: set shutdown_announce_in_ms to 0
test: test_tablets_parallel_decommission: prevent group0 majority loss
test: delete test_service_levels_work_during_recovery
3adf8b58c4