Prepare for Flex Extras in default_engine
Prepare for Flex Extras in default_engine

Change-Id: I81b95c917f7755e2d134f76fdd50f16357a15d2c
Reviewed-on: http://review.couchbase.org/101723
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