MB-15732 Bucket validation is not required for stream cleanup
MB-15732 Bucket validation is not required for stream cleanup

MergeStream is only going to DelBucket/CloseStream for which bucket
validation doesn't matter. This is only projector level cleanup.
This logic is now same as StopBucketStream which also doesn't do
bucket validation.

If a bucket has been deleted/flushed, DelBucket call from projector
will return success.

Change-Id: I178d89dc5b4a620ba13bdfbaef6ae374a789a63a

jchris/indexing,jchris/indexing,jchris/indexing,jchris/indexing