MB-15699: Assert that chkpt is not closed for replica vb until snapshot end.
MB-15699: Assert that chkpt is not closed for replica vb until snapshot end.

When we are processing streamed items for a replica vbucket, checkpoint
should not be closed until all the items in the snapshot are processed.
In this commit we are asserting the above condition in queueDirty()
func in checkpointManager and also logging a message.

Change-Id: I6d14bc0df57d685faaa3ee002012090a6e67c2d9
Reviewed-on: http://review.couchbase.org/53311
Reviewed-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>
Tested-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>

couchbase/ep-engine,owendCB/ep-engine,hisundar/ep-engine,couchbase/ep-engine,teligent-ru/ep-engine,membase/ep-engine,hisundar/ep-engine,daverigby/kv_engine,membase/ep-engine,hisundar/ep-engine,couchbase/ep-engine,daverigby/kv_engine,teligent-ru/ep-engine,teligent-ru/ep-engine,teligent-ru/ep-engine,owendCB/ep-engine,daverigby/ep-engine,couchbase/ep-engine,owendCB/ep-engine,daverigby/ep-engine,daverigby/ep-engine,membase/ep-engine,daverigby/kv_engine,hisundar/ep-engine,daverigby/kv_engine,daverigby/ep-engine,membase/ep-engine,owendCB/ep-engine