Once current window is sealed, TWCS is supposed to compact all its
sstables into one. If there's ongoing compaction, it can happen that
sstables are missed and therefore past windows will contain more than
one sstable. Additionally, it could happen that major doesn't happen
at all if under heavy load. All these problems are fixed by serializing
major on past window and also postponing it if manager refuses to run
the job now.
Fixes#9553.
Reviewed-by: Benny Halevy <bhalevy@scylladb.com>
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>