MB-9484: Move all functions out of TapProducer class

Change-Id: I1332619f132b2980962e21d6eb43984f7a4bbb51
Reviewed-on: http://review.couchbase.org/30846
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>