Truncate nemesis - Flushing files before truncate
Truncate nemesis - Flushing files before truncate

In order to workaround issue #4924, try to flush memtables.
This should allow truncate to finish quicker.

scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests