Update the regular expression in `check_node_log_for_failed_mutations` to avoid
false test failures when DEBUG-level logging is enabled.
Fixesscylladb/scylladb#23688Closesscylladb/scylladb#23658
When we remove a node in the Raft-based topology
(by remove/replace/decommission), we remove its
tokens from `system.topology`, but we do not
change `num_tokens`. Hence, the old check could
fail for left nodes.
We extend `start_writes` to allow:
- providing `ks_name` from the test,
- restarting it (by starting it again with the same `ks_name`),
- running it in the presence of shutdowns.
We use these features in a new test in one of the following patches.
