Test was failing because _qp (distributed<cql3::query_processor>) was stopped
before _db (distributed<database>).
Compaction manager is member of database, and when database is stopped,
compaction manager is also stopped. After a2fb0ec9a, compaction updates the
system table compaction history, and that requires a working query context.
We cannot simply move _qp->stop() to after _db->stop() because the former
relies on migration_manager and storage_proxy. So the most obvious fix is to
clean the global variable that stores query context after _qp was stopped.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
36d31a5dab