Refactor: clean up initialization of SubdocCmdContext
Refactor: clean up initialization of SubdocCmdContext

Change-Id: Id801ecba1881bea5c96c2b3238c4640f843be7ba
Reviewed-on: http://review.couchbase.org/85772
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine