Disambigute messages from indexing DCP consumer

Change-Id: I48df7ce464c6ebe736514c401b6138490e56dc00
Reviewed-on: http://review.couchbase.org/43686
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Sriram Melkote <siri@couchbase.com>
Reviewed-by: Sriram Melkote <siri@couchbase.com>