CBLT-198:  comment out $request->content_type('text/plain') in put request

Change-Id: Ibc803ce9fed47317afbd1ad3d606dab1452416dc
Reviewed-on: http://review.couchbase.org/34138
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>