Drop and recreate collection when flush collection.
Drop and recreate collection when flush collection.

Currently, beyond.ts just remove all documents on test. But now we have to
test index. So this patch makes recreate collection instead of just removing
all documents.

SollmoStudio/beyond.ts,sgkim126/beyond.ts,sgkim126/beyond.ts,SollmoStudio/beyond.ts,noraesae/beyond.ts,noraesae/beyond.ts