Fixes: SCYLLADB-244
Disables snapshot control such that any active ops finish/fail
before proceeding with decommission.
Note: snapshot control provided as argument, not member ref
due to storage_service being used from both main and cql_test_env.
(The latter has no snapshot_ctl to provide).
Could do the snapshot lockout on API level, but want to do
pre-checks before this.
Note: this just disables backup/snapshot fully. Could re-enable
after decommission, but this seems somewhat pointless.
v2:
* Add log message to snapshot shutdown
* Make test use log waiting instead of timeouts
Closesscylladb/scylladb#28980
a5df2e79a7