MB-29238: Use domain instead of source for memcached audit events
MB-29238: Use domain instead of source for memcached audit events

Change the memcached audit events to have a user_id made up from
{domain, user} as opposed to the previous {source, user}.

Change-Id: I02b7e2027d2cc4777386ca7550de8c503a083389
Reviewed-on: http://review.couchbase.org/92613
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