MB-100: revised mixed dgm with read hot load phase

Change-Id: I0ea8b63c1ac32f60a1c9699eadf9a163957db4cd
Reviewed-on: http://review.couchbase.org/27319
Reviewed-by: Ronnie Sun <ronnie@couchbase.com>
Tested-by: Ronnie Sun <ronnie@couchbase.com>