MB-11394: Disable use of the datatype feature

Introduced a new configuration attribute in the configuration
to enable it: "datatype_supported" : true

Change-Id: I0de2f5315de94eec14670218505dc36406303f3d
Reviewed-on: http://review.couchbase.org/38228
Reviewed-by: Dave Rigby <daver@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>