When flushing is done externally, e.g. by running
`nodetool flush` prior to `nodetool compact`,
flush_memtables=false can be passed to skip flushing
of tables right before they are major-compacted.
This is useful to prevent creation of small sstables
due to excessive memtable flushing.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>